There are two ways to search for first floor primary bedrooms. It is recommended to use only one of these per search.

On the residential search page, you can use the checkbox, to search listings that used the room information to denote the first floor bedroom:

Otherwise, you can use the Interior field options to search, after adding the field:

If you want to search comprehensively for listings that have used one or the other, it is recommended to build two searches/auto emails to do this. This will capture any listing where the listing agent used one or both.