You press Y or Triangle when you are looking at the body, close enough to see their inventory

At what level did you do it at? There is a HUGE glitch surrounding this, saying that if you do it too late or if you do it at too high a level, he will never call you back and will never upgrade your armor. I did it at level 11 and you are supposed to be called back at level 15 for the first upgrade. I've tested it…