When you particularly enjoy a specific Member's music and are regularly reposting their work, you can add them to your Starred List by clicking the star under their name on the Earn Dashboard:
If you so choose, you can remove them from your Starred List whenever you like by clicking the star again:
To send music to your starred members, go to the Promote Dashboard, make sure you're on the Direct Requests tab and open the filter:
Then toggle on "Show starred members only" and Apply Filters:
You will then only see your starred members in the list of members to send direct requests to.