1997 Daihatsu Charade Door lock

I am still new to the whole car tech side of things so please be patient with me. I have just replaced the passenger external door handle and everything seemed to work fine until I closed the door, which then I was not able to open it again from either the inside or outside door handles. I was able to eventually open the door and found that the problem was the door kept slightly locking every time I tried to use one of the door handles. I compared the passenger door to the drivers door, which works fine, and found that a moving part that is supposed to push down onto a connector to the external door lock keeps slipping. I can see the problem but I dont know how to fix it.