Inclusion Criteria:

• - Diagnosis of fibrotic ILD.

• - In possession of a smartphone/tablet.

• - Able to understand written and spoken English.

• - Adequate digital literacy to complete requirements of trial.

Exclusion Criteria:

• - Not in possession of a smartphone/tablet.

• - Insufficient digital literacy to complete requirements of trial.

• - Unable to communicate in written/spoken English.

• - Not on stable ILD treatment for 30 days prior to randomisation.

• - Participating in pulmonary rehab at enrolment.

- Unable to provide informed consent

This study compares REBUILD-SM with standard care in people with ILD. REBUILD-SM comprises a purpose-built smartphone app that allows subjects to enter and track health data over time and an integrated self-management website. Participants will enter their respiratory diagnosis, medications and side effects, weight, lung function test results, oxygen saturation level and supplemental oxygen usage into the smartphone app. They will also use the app to answer questionnaires at specific timepoints. Participants will input most of this data at the beginning of the trial and then update it when it changes, for example, after obtaining a new lung function result, starting a new medication or getting a new side effect from an existing medication. Entering data into the app is expected to take around 30 minutes at the start of the trial, and about 20 minutes at 12, 26 and 52 weeks when completing the questionnaires. Updating data is expected to take about 5-10 minutes and will only happen when there is a change, for example, once per week, although it may not be this frequent. The app will not provide any recommendations on the health data participants enter

• - it is simply for recording purposes.

To ensure data collection is as complete as possible, electronic reminders will be sent when questionnaires are not completed at the specified timepoints, and app analytics will be used to monitor use of the app and will alert the study team if the participant fails to complete the questionnaires in response to the reminder. This will prompt a phone call from a member of the study team, but this is the extent to which app analytics will be used during the trial. App analytics will be used in the data analysis phase (after the trial is over) to understand how participants engaged with the app. Participants in the intervention group will be asked to log into and use the self-management website with support from the study team. The self-management website includes 12 modules and has been designed in collaboration with people with ILD to help increase their ability to self-manage their chronic disease. During the intervention period, participants will receive four phone calls from a health professional involved in the management of people with ILD to help them set health-related goals and identify appropriate modules from the website to help participants achieve these goals. These four phone calls are expected to take about 15-30 minutes each. Each module provides information regarding the topic and provides access to relevant websites, fact sheets, booklets, videos and webinars as well as other external resources. Participants will have direct access to these external resources from within the package through hyperlinks embedded in the title of each resource. Participants are expected to work through their selected modules at their own pace

• - there is no specific amount of time they are required to allocate to the intervention, and they can utilize as many or as few of the resources as they like.

Adherence to the intervention will be monitored solely through the four phone calls and is participant-reported.

Arms

Experimental: REBUILD-SM Group

Participants randomised to REBUILD-SM will receive the self-management package as well as the RE-BUILD app. Structured self-management support via telephone or Zoom call will be provided 4 times during the 12-week intervention period.

No Intervention: Standard Care Group

In the control arm, participants will receive standard care and a reduced capability version of the RE-BUILD app to be used for data-capture only. They will also receive phone/Zoom calls at the same frequency during the 12-week intervention period, but no health advice will be given. After 26 weeks, participants in this group will receive access to the fully functional RE-BUILD app.

Interventions

Behavioral: - Pulmonary Fibrosis self-management package and smartphone application

The pulmonary fibrosis package includes modules on understanding treatment options for pulmonary fibrosis, managing medication and side effects, understanding and accessing clinical trials, managing shortness of breath, managing fatigue and mood, managing co-existing conditions, the role and importance of pulmonary rehabilitation and regular physical activity, role of oxygen therapy, smoking cessation advice and support, accessing community support, and communicating with others when living with pulmonary fibrosis. The RE-BUILD app is used as a tool for data collection and to help participants track their health over time. Participants enter their health data, including baseline conditions, medications and diagnosis, pulmonary function results and supplementary oxygen use. It also tracks air quality data and physical activity via the phone's step count and has links to ILD-related educational resources.