I change my password on my i cloud account and my apple id, now my I phone 12 I couldnt sign in

kokang_64 Siad:

"I change my password on my i cloud account and my apple id, now my I phone 12 I couldnt sign in: I bought an I phone 12 from my friend and its unlocked. I set up the phone and it was successfully signed in. The next day I forget the password that i created, and it was locked out. [...]"

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Handing an iPhone Over Properly:

Give this back to your friend. Then, nave your friend perform as instructed here, including the iCloud logout: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support