Use Face ID or Touch ID if it is already set up and working
Try the correct passcode if you remember it
Use iCloud Find My iPhone if the device is already trusted and you need to erase it remotely
Use a previously trusted computer to back up the iPhone and restore from backup if needed
Contact Apple Support with proof of purchase for account and device recovery options
If the iPhone is managed by an organization, contact the administrator
If none of the above works, the iPhone cannot be unlocked without eventually erasing it