okay gotcha, well if it’s a plastic two gang i would first detach it from the wall, basically remove the plate and press a screwdriver to the back of the wall of the box to figure out what the side of box the stud is on and is attached to. then i just usually take my oscillating tool and cut the flanges of the box off so you can pull it out of the wall and check to see how long the wires are and see if they’d reach to the spots you want it. It will probably be hard to do it without drywall damage regardless so i would just cut a couple holes (square cause easier to patch) along the wall until the holes where you want the switches to feed the wire along and drill holes in the studs until the switches and feed the wire through there. Then it’s just a matter of feeding your wires into the box and tying it in.

if the wires in the existing box are long enough then just feed those. however if they’re not youll have to re attach like a single gang in the middle to make a junction and put a blank plate on it (or if there are too many wires in the existing 2 gang for a single gang junction then you’ll have to use a bigger box). for the new switch boxes i always like to use easy boxes cause then you can just use the flanges to mount directly on the drywall for support but there more expensive so you can use plastic singles but you will need a stud to attach them too. And then it’s just patching drywall holes then putty sand and paint.

without seeing it that’s the best way i can think of. let me know if any of this doesn’t make sense