You must first reset your tracker to unlink it from your account.
In the app, to leave your account:
MENU > Set up my devices > AM3 > Reset.
This reset erases all your personal data from the tracker, including unsynchronised data. So be sure to synchronise your data with your iHealth account before this reset.
You will not lose previously synchronised data.
If you do not know which iHealth account is linked to your tracker (unknown, forgotten, etc.) please contact our support team.