On some of the more compact models of wireless mice (at least with my Logitech), the clamshell of the top is partially hooked onto the bottom. If that’s the case, there will be only two tiny screws under the rear slider “feet” stickers of the mouse but no others. Remove those screws, and pop the rear open by only 2mm or so. And that’s as far as it goes so don’t try to pry it open any further in that direction. Now push the top half of the clamshell forward vs. the bottom half. (Like you’re trying to shear it along the plane of the seam between the halves.) Should unhook at the front of the mouse and easily come open the rest of the way. Be careful when doing this. There may be wires going to the upper clamshell half for things like lights, and you don’t want to damage them. The rest of the mouse should now be accessible for cleaning the inside. Putting together is kind of the reverse, catching the hooked end first and then pushing the tail back down before screwing it together.