Iram, is the slide locking lever going in all the way? I just stripped my neighbor's 6906 and I could only get it to go all the way in after lining it up with the slide notch. This notch servers to purposes. First, the locking lever slides into it to lock the slide back and second it allows you to remove or install the locking lever.

Also, the recoil spring notch is the really small half moon cutout on the barrel. It's so small that I didn't believe it would hold the tension but it does.

Take your time you will figure this out.

Let us know your progress.