Hi, @mars13 I would suggest trying to change it on the web based Fitbit platform. There is a link to the web based platform on every page when you are logged into these Fitbit Community Forums. Go to the top of the page and click on “Dashboard” top right. Next click on the gear icon also top right on the dashboard page. That will take you to the personal account settings and you can change your birth date there.
I hope this helps. Welcome to the forums!
Sense, Charge 5, Inspire 2; iOS and Android