Unless you're willing to sand down to the wood they may not come out.

It looks like the ball trail has worn through the topcoat and the paint is exposed--no amount of sanding or abrasive materials will "remove" the wear. It's common on games that have gotten a lot of play. There's not much you can do about that without clear coating the playfield and repainting it. If you try to repaint it as-is, it will probably look worse.

Wax it, maybe cover it with mylar to stop it from getting worse (although this may hinder future restoration efforts), and then play & enjoy it.