48 hours - never figured out how to play this one part on guitar

hey y'all! So, I've loved 48 hours for YEARS, and have tried to learn to play it many times. I've succeeded, mostly, other than ONE part (most clearly illustrated in a live video), which you can see in this video here. Timestamp at 2:12 if it doesn't go automatically.

What the hell is the chord shape he's using to slide like that? Do your strings need to be looser, or is there a slightly different tuning?

If anyone can answer this for me and slay this beast, I'll be so damn grateful. I've asked most of the guitar players I know in real life and all of them are baffled lmao.

thanks all <3 <3 <3