You might look for a parts listing for that control. It might tell you what comes apart.
To remove the throttle handle, as was suggested, sometimes an Allen set screw holds it. Om mine, the handle needed to be about 75% of max throttle in reverse (engine off, naturally) to gain access to the Allen screw, on the very bottom of the handle.
To replace the trim switch, many controls have a couple of screws holding a plate over the switch access. I don't see that on yours.