I watched several youtube videos on the subject before giving it a try and wasn’t impressed with how much difficulty the folks making the videos had with gettting the xmitter to pop out.
Upon doing it myself for the first time I soon discovered the difference in technique between success and failure: If you are using a test strip, be sure than the strip is pushed down into the gap ALL THE WAY until it hits bottom, and then slide it from the rounded end of the xmitter, towards the opposite end. Start where there is a vertical slot (it’s where the sensor bends 90 degrees when a xmitter is removed with the sensor already removed from the body. The xmitter should pop up as you drag the strip along. Then go to the other side and do the same thing. The xmitter should pop right out.
If you think you have inserted the strip deeply enough, but you actually didn’t, you may be fussing with extraction for some time.