Welcome to Android Central! You can't reset the PIN -- it wouldn't be a very good security measure if you could do that easily. Google's Find My Device will only allow you to remotely set a PIN if the phone didn't have a screen lock set in the first place. You'll have to do a complete factory reset from the Recovery Menu (which will require you to enter your Google account and password as well -- hopefully you remember that), but unfortunately that means all local data will be wiped. Were you backing up or syncing important information on a regular basis?