How to restart iPhone 11

Restart: Force restart iPhone - Apple Support

Reset: If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

Re-home: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

If Activation Lock is somehow involved here, that mechanism is intended as a theft deterrent, and is not easy to bypass. Contact the seller and request that lock be removed, or a refund. We can’t help you with Activation Lock removal, and—absent convincing proof of ownership—Apple won’t.

Restart or reset? You have asked two different questions.

Restart simply powers off the phone and then powers it back up again.

Reset erases the data on the phone, then it starts up to the "hello" screen so you can set up the phone again.

Maybe if you could tell us what kind of difficulty you are having, we could suggest the right approach.