do you have a polygon layer to join by using one of your fields?
Join Field (Data Management)—ArcGIS Pro | Documentation
The field name doesn't matter, it is the contents of the fields that you are using to join that needs to be the same. (eg A to A will work between the two fields, but A to a won't)
I figured I couldn't join by A to a. I ended up downloading a list of the counties, adding that to the excel file SNAPCounties, adding it to GIS, then combining it with my polygon layer USCounties. That method worked, but it was annoying