Try practicing with a recently removed sensor with the transmitter still attached. Put it on a flat surface in front of you and practice using the removal key. You must insert this key at a very specific position. Take note of the tool’s position relative to the printed graphic on the back of the transmitter. Of course, having a flat table to push against (and using a second hand!) makes it easier but it is possible to do on the back of your arm with some practice.
I’ve only done this a few times and each time required some repeated efforts. If a personal assistant was available, I’d likely choose that route first.