WATCH THE ENTIRE VIDEO BEFORE REPLAYING TO ACTUALLY TAKE ANY OF THE STEPS! You should note in his title it says, "3DS XL Top LCD Screen Replacement and Teardown Tutorial.: In other words, he's going to tear it down in its entirety first, then he shows how he removes the top screen for replacement - you do not need to take all those other steps if you're only replacing the top screen ;) Good luck!
https://www.youtube.com/watch?v=qWmoXDuUylw