As outlined by Hashish, for weighted wrist flexion and extension, you want to keep your elbow at roughly 90 degrees, keep a weight in your hand, raise your hand, and then gradually reduce your hand. The pain is worse when arms are straight so you try and flex your wrists https://www.theorthopaedicandpainpractice.com/how-to-alleviate-tennis-elbow-pain-tips-from-a-medical-expert/