Open the individual member record, then double-click the Role record shown in lower left of the Member form. This will open the Role dialog where you can change the current Club Name assignment. Click Save and Close and the session (aka attendance) records will be updated to reflect the new club name from the current club date forward. (Tip: If you want the club assignment change to be effective on a particular club date, make sure THAT is the date you have selected as the Current Club Date in the main toolbar.)