Re-Pair Your Challenge App to Another Google Fit Account
1) Tap the menu button in the upper right corner of your Challenge app, and choose Account Settings (Image #1).
2) Scroll down and view your 'Tracker' step source (Image #2). If you would like to pair to a different step tracker, tap "Unpair" and then follow the instructions listed on Pairing Google Fit with the Challenge app.
Note: when you pair to a new step source, only steps you take after you pair will be credited (i.e., you will not receive steps taken prior to pairing to your new step source).