Currently, Search Within is only available in the classic search experience, not redesigned search.
Searches within the Acquia DAM can be completed when a search term is entered in the quick search and keywords are entered in the Search Within box in the refine search.
If you're a DAM admin, you can select to have the Search Within box display either at the top or bottom of the Refine Search area. This can be configured from the Refine Search settings in the Admin app. Under Document Search Position, select top or bottom.