Do not confront the guest. Take a picture of the broken lock then contact Air BNB and request guest to be relocated elsewhere. Give guest a time requirement for leaving such as 2 hours and remain in the space while they pack up to keep guest from retaliation damage. Allow refund according to your cancellation policy. Do not try to negotiate with the guest but reinforce the expectation they leave. Flag the profile of guest.
This is a difficult situation for any host. Good luck and let us know how it all turns out.