Sorry not quite clear on what happened here.
Are you saying the guests have stayed past check out which should have been yesterday and not checked out or returned your keys @Gemma213
I presume you have already tried to reach them by phone and Airbnb messaging to tell them that they need to return to collect their things and give you the keys?
Presuming you have contacted them:-
1. call Airbnb and tell them what has happened and that you need to clear their room for future guests
2. Contact the guest again and tell them they need to return to collect their belongings. If they have no belongings their let them know if they don't return the keys today you will need to charge them to change the locals
3. Send them a request for the cost of changing the locks and leave them an honest review.