STUCK CHOKE TUBES
I’m tempted to say: “With very great care”, because undue force can do damage.
The first thing to try is a good, long soak over several days in either penetrating oil (obtainable from car accessory shops), or diesel.
If the tube cannot be removed with the key after that, then take the gun to a gunsmith.
It just isn’t worth the risk of damaging a good gun by employing a DIY solution.
You can prevent choke tubes getting stuck by removing them for a thorough clean every time you clean your gun, and re-fitting them with a smear of grease on the threads.