Blast+ blastx search database file selection


Can anyone provide advice on what files to use for Blast+ blastx reference? I uploaded the most recent NCBI non-redundant protein sequences (nr38 - updated 5May2020), but none of the files therein are allowed as options for the search database. I believe I shouldn’t need to do the makedb step first, as these are pre-formatted database files, but please correct me if I’m wrong! I appreciate any advice you can provide!

Thank you!