Unless it's quite an old phone a factory reset will just make it worse (unless you know their Google account username and password). The "factory reset protection" system is an anti-theft device intended to deter thieves by preventing them from just resetting a phone to get past a screen lock. On some phones there are ways of getting past it (which the manufacturers patch as they are found, so older, unupdated phones are more likely to have such a bypass), but for obvious reasons posting ways to defeat an anti-theft measure in a public forum is a bad idea.
And of course if there was a way past the PIN without a reset then factory reset protection would be useless. Actually someone posted here recently about how a particular lock-screen app allowed them to bypass the screen (i.e. they entered the app from the lock screen and could then leave that app and enter the phone without being asked for a PIN), but I think this was probably a manufacturer bug rather than a general feature (I've never found such a thing to work on any of my devices).
