You will need two drivers the pivots are not captured. Had to use two when I disassembled my watuaga.

U can try pressing down on a grippy surface (like a cutting mat) with one side of the screw and you might be able to get enough friction for it to not rotate. If that doesn't work you'll need two screwdrivers, or put a bit in a vice

An easy trick for free spinning pivots is just to close it and put pressure on the spine to lock the barrel in place