You don’t need to! The Breathe app talks directly to Fitbit’s servers in order to retrieve activity, sleep and resting heart rate data. You just need to make sure that you synchronise (sync) your fitness tracker with the Fitbit app regularly, so that Breathe can collect accurate and up-to-date metrics from the Fitbit server.
Fitbit needs the Fitbit app to be open when you stand on your Fitbit scales, so that the data is synced across. Open your Fitbit app and stand on your scales once more.
In Breathe app’s ‘Settings’ page, tap ‘Connected services’, then ‘Fitbit’ and check that you are connected. If not, follow through the process outlined in the Fitbit guide. If you are connected, open the Fitbit app and force a sync. Check your data preferences, and make sure Fitbit is the selected data source of choice.