I presume this is the video you spoke of.
https://www.youtube.com/watch?v=FqN-FmskIMw
Do that backwards. If that doesn't help you, maybe try following a RS hk45 video. I've never dealt with the hk45 so I cannot say how similar they are.
Try here?
https://www.youtube.com/watch?v=BEwh...750663D5817F32
If that doesn't work, you have 3 options.
1) Contact a few gun doc's and see if they can help you.
2) sell it for cheap on the forums.
3) mash the parts together like a wallaby on meth & hope for the best.
For future reference always try to find a video / source of info before you start tearing stuff apart...or you're going to have a bad time.
best of luck - alex