pull out this adjustable arm piece out of the headband

Unscrew the wire free from the adjustable arm piece, letting the arm spin freely around the wire.

screw the adjustable arm piece back on-to the earcup arm, in my case there was some resistance from a lip on the screw that prevented it becoming unscrewed in the first place. i was able to gently push past it multiple times till it was screwed on snugly