ill try to help,
ok firstly this glitch is easier to do if
1- you have raygun or balistic knife equiped.
2- Dive close to the wall near the arrow
3- if you land on the wall but can not move try standing up(this confused me the first time lol)
4- its NOT patched
this glitch is VERY tricky to do but if you follow these steps you will find it a little easier
dont forget to thank if this helps