Apple ID not working properly

The phone I’m using right now is a phone signed into another persons Apple ID and I tried to sign them out of it but it’s not working, it doesn’t have anything anywhere saying that they are signed into this phone but when I try to update or download something, it says my passwords wrong even though it’s correct. Eventually it takes me to a screen saying “forgot password”, I click on it and it gets me to sign into their account but I not know their password. So I put my email in and than I put my phone number in. It sends me to my other phone and than I try again and I have to do je exact same thing