For that optic it’s Listed in the specs as M3-0.5x10mm, if the plate requires a different size it should have shipped with them or the plate manufacturer should offer a replacement screw kit if you misplaced them.
Word of advice though, if possible use hardened steel screws when using an adapter plate. I had a screw from C&H shear off at the slide due to recoil after putting on one of their plates, had to have it re-tapped and during that process the other one sheared.