help! my AppleID shows on my iphone7 but wont accept password even though I changed it several times. My grandson had my old iphone6 and signed in with his email which when I go on app store keeps coming up but dont have a password.

My grandson had old phone and signed into with his email... I cant access my apple id as it wont accept new password even they I keep requesting new one and changing it wont work it says.....unknown error.

It has my email on my apple ID but when going into app store it has grandson email. I have gone into my apple accounts but only shows my email saved?

cant use fitbit or any apple store- help would be appreciated