There’s a series of orthopeadic tests call upper limb tension tests (1-4) designed to target different nerves. Most of them involve winding your arm up in a certain position which will put a stretch on the nerve then moving your head away from it (either rotation or lateral flexion depending on the test). Brachial nerve flossing would be along the lines of loading up the arm then doing small pain free motions of your head in the recommended direction to gently tug at the nerve freeing it up and hopefully helping with your issue.