If it's the one in the mind stone then it doesnt work. If it's the one in the reality stone then heres how to use it. First, left click on a npc, then click on another npc and it will change their body shape, NOT their appearence.

The one in the mind stone does work. It takes the appearence of whatever entity you're using it on and makes you look like it. It isn't noticable in first-person. Pressing L-Shift while using it will restore your character's appearence.

Thanks! got it now.

Mine doesn't work. It just turns me into the npc for a second before reverting to my playermodel, even when I hold it. Help ?

Holding L-Shift changes you back. Unless you keep changing whether you're using L-Shift or not, then that shouldn't be happening.

it doesn't switch me back and forth, it only works for a second.

well L shift doesn't work at all

Nevermind, mine magically resolved itself.

Reality Stone version - pressing and holding L-Shift doesnt't turn NPCS or player back, any help?