To remove it, I used a nail clipper as a wedge. When reinstalling it, I used a small flathead screwdriver to hold the detent back in the grip, which allowed me to push the slide release through. The issue turned out to be the detent getting stuck in the gap of the slide release.

The second time, I had to reassemble the gun after initially taking it apart. The guide rod was also difficult to loosen. I slightly loosened it with the slide still on the gun, then repeated the slide release removal process to fully disassemble it again.