P239 SAS question - re-installing locking insert

Got a newbie-to-P239 question, would appreciate your kind help. I took off the stock TDL so I could install an AC Sport version, and was not expecting the locking insert and slide catch lever spring to pop out of the frame. I can figure out the basic idea of where it goes back in, but cannot find any way of angling it or putting it in from top that fits it back into the frame. Feel like an idiot to have to ask, but after scouring this site and the web for any hints or instruction on this step, I can find no insight and am stumped. Photo below shows the frame and the locking insert with slide catch lever spring next to it (the latter turned sideways for the photo).

Any suggestions, or pointers to a resource that can enlighten me to complete what I naively thought would be a 5 minute task? Thank you in advance!