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[Mimah]

Previous owner did not delete his email. This phone is still under his email, so I can not use Sa3msung products. 

I do not know where is he.

[bruunduun]

I'm pretty sure you can factory reset a phone in recovery mode not through the settings where you need a password

[GalaxyA51user]

Reset your device and remember the lock screen pattern (maybe PIN or Password) to unlock your device otherwise you need to enter email of your previous owner. (If you don't know any of these, use any FRP unlocker on PC)

[Pugs1957]

If they didn't remove their Google account there's nothing you can do.

[GlenRobertson]

Add your Google email and account then delete the old email account.

[N1NJATH3ORY]

Don't factory reset it does not wipe email you will be fully locked out add second email address then try to remove original email account

[N1NJATH3ORY]

Wrong it don't no matter what type of reset you do it ask for email password before first boot! Bad advice..