A renter can initiate a cancellation by following these directions in Airbnb, https://www.airbnb.com/help/article/169.
An owner can cancel an Airbnb reservation by logging into Airbnb and following these directions, https://www.airbnb.com/help/article/50.
For Vrbo reservations, the cancellation must take place through MyVR by the owner. Go to the reservation and from the "Actions" dropdown, select "Cancel reservation." Follow prompts and select an accurate reason for cancelation. The renter will be notified of the cancellation in 24 hours in Vrbo.
Cancellations should be made in the TripAdvisor dashboard by the guest. For directions see, https://www.tripadvisorsupport.com/hc/en-us/articles/115000304927.
Additional TA support content can be found here, https://rentalsupport.tripadvisor.com/articles/FAQ/Canceling-a-booking.
Guide the renter to request the cancellation in booking.com by following these directions, https://partner.booking.com/en-us/help/reservations/if-guest-asks-me-cancel-reservation-what-action-should-i-take-extranet
Additional Booking.com support content can be found here, https://partner.booking.com/en-us/help/reservations/can-i-cancel-reservation.
Owners can request cancellations on behalf of a guest in the Expedia partner portal. See https://apps.expediapartnercentral.com/lodging/help/help-article/guests/cancellations-and-no-shows/cancel-a-reservation.
Go to the reservation and from the "Actions" dropdown, select "Cancel reservation." Follow prompts and select an accurate reason for cancelation.