You have to remove that black plastic spring cover on the back of your slide. In the upper right side I believe is a small gap that will allow you to pry that spring cover. I used one of those tiny screw drivers to get it to start moving. Once it starts to move. STOP You should be able to take it the rest of the way with your thumb. You will want to do this slowly and make sure to hold on to over the opening as you will have a striker spring under that cover wanting out.
I usually kept my free hand over the cover to catch the spring once it's released. To replace it get the parts in, get the cover started then use a small screw driver to hold the spring while you slide the cover back in place.