Unable to set up new account on my MacBook Air

"Unable to set up new account on my MacBook Air: I’m setting up a new account on a pre owned air. When I tried to make a new account for the laptop, it wouldn’t create a new account due to the name. I tried several variations but none worked. I then restarted the laptop and all of the accounts I attempted to create were loaded on the Home Screen but I am unable to log in or reset the password for the accounts."

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Return and Get this Logged Out:

Where did you purchase this? Return it, and have the seller perform as instructed here, including the iCloud logout: What to do Before you Sell, Give Away, Trade in, or recycle your Mac - Apple Support. The seller should have known better.