the push arm clicks into a rectangular slot. The push arm looks like an up and down staircase
Dave Sr. from SWISCO responded:
April 11, 2022
I'm afraid I can't get a good look at the part needed from this photo but you can start by taking a look at the 26-312 thumb button activator, along with the 26-211 top tilt latch to see if this is the part you are looking for.