@Heather2043
The only way to indicate you have a King bed is in the Photo Tour under sleeping arrangements and you can list it in your Title. Airbnb has an on-going issue with showing listings correctly that do have a King bed when the filter is used.
You'll need to contact Airbnb and have them correct this as if you have a King bed listed in the photo tour, you listing should appear when the King bed filter is selected by a guest when searching.