I pinch and pull, it does take a little effort be careful not to pull too hard though. To re insert just push back in and you’ll hear a snap.
Yes, this can be a little tricky. We didn’t want to make it too easy to pull out directly so we designed it so it has to be rocked side to side to get it out. Hold the unit in one had and use the other hand to push the mouthpiece to one side. You will feel a little click as it moves to the side and then you can pull it out. I hope that helps!
Hold the Firefly with the mouthpiece pointing away from you, push the mouthpiece firmly to one side, and you will feel it click out of place. To replace, place one side in and click in firmly to the other side. We also have some photos and directions in our user manual: