If they come early and want to stay on, you can only tell them to book elsewhere before their booked days. Or offer any days between current guest and their arrival date at normal rate. If I can, I'd help them with wifi and phone calls.
If they come now instead of later, they still have to find a place and have to cancel yours. Depending on your cancellation policy, you will lose money on that. In the second case, I would not be helpful, even with information,as the longer they wait with cancellation, the less you will lose. I would however inform airbnb, that they showed up early and left. Prevents future lies...