I usually insert the non-attached end first, the push the attached end in.

If that doesn't work, give it a good yank and rip it off. Don't really need it.

 

I'm debating ripping it off myself... I used to think I needed it, but the last couple phones I had didn't have it, and miraculously, I never managed to kill the phone.

 

There is no need to rip it off. It works similar to the way to you put on a face plate for a car stereo head unit.

The little piece of plastic that is attached to the phone slides inside the phone. Slide it in all the way to the left and the free end should snap right in. You have to give it a pretty firm push to snap in, but once it goes in it is sealed up pretty tight.

I actually kind of like it that way.