Use Face ID or Touch ID if it is already set up
Use the correct passcode if you remember it
Use Apple ID recovery if the device is locked and you forgot the passcode
Erase the iPhone with Recovery Mode and restore it from a backup
Use Find My iPhone to erase the device remotely if it is linked to your Apple ID
Contact Apple Support with proof of purchase if you need help regaining access
If the iPhone is managed by an organization, contact the administrator