To do this glitch take cover on something that you can switch cover with... like switching from one wall to another & after you do that come off of cover & then tap A,up,A really quick afterwards, & then you should be in the glitch... & if you have a long wall next to where your crouching/standing then turn your screen to the left or right depending where you standing/crouching & you will slide down the wall.
P.S. Srry for not having any videos... i probably won't have none for a while. And if you need any help with the glitch my gamertag is icetactic