From what I’m seeing you use the ring finger for the 13th fret on the low E string. So 13-12-10 are fingers 3-2-1 respectively, where normally I would use the pinky on fret 13, and then ring and index for 12 and 10.
I’m curious because out of all the things in the Antigravity seminar this is the only one I am having trouble getting clean and I’m not sure if scale length has something to do with it.