The question of improving legendary weapons (Middle-earth: Shadow of War)

Plz tell me. Here for example is written by the type to improve weapons recruit Orc LVL 20 and above from the tribe X. I've recruited not one, but to improve things you can't. It is necessary to make recruitment to this thing was wearing or better weapons after what mission will be? (Right now I'm on the 2nd act run, pressed the fortress of the Instigators) . Higher weapons have improved without problems