I am trying to put the glass back on my side mirror I bought the part from junk yard but i cant seem to get it back on because of the L shaped prongs that control the mirror moving left right up and down this is a non heated mirror, Can anyone tell me what im doing wrong. The plastic part just keeps popping off.

 

the circle part in the lower picture should be attached to the mirror motor. It looks like it is no longer connected I think when that piece comes off the mirror, you will need a new mirror. I have never had that piece come off, when it does, the mirror is usually junk.