It's part of its history, timber never stops moving, I would just leave it.
I was an antique furniture repairer back in Edinburgh and the Queens residence Holyrood Palace got central heating in about 1972 and a Tudor oak table that had been there for 100's of years split open due to the dry air.
in extreme clock restoration, tom temple says it's possible to straighten plates of wood movements by re-introducing moisture to the concave side of the plate using a damp towel, and then clamping plate and towel straight to a piece of wood.... but wood movement plates don't have glass in them, and probably aren't sealed with a finish like this door.
probably best left alone... but i empathize with another one of those 'small things about my clock that bug me' moments.
I know. There's no easy way. I'm a a bit surprised the glass hasn't cracked. Still I plan on trying. I know why it happened. When I purchased the clock years ago. Even than closing the door was an issue. I was too focused on getting it up and running to notice the doors center hinge was missing. Hence dry air and time has worsened the issue. My bad. Was looking for possible solutions that I might not know about. Thanks for your response.
It looks like it is warped pretty bad with a bow in the middle. If it is so bad you need to straighten it, you can try removing the glass and laying it on concrete with the center warp upwards and cardboard protecting each corner. Then place a brick or some other weight in the center of the bow and use a steamer to add moisture and heat up and down each bowed piece. Leave the weight on while it dries and cools. You may have to do this several times to get the bow out. Then you will probably need to refinish. I have also used this method to straighten bowed pendulum rods on long case clocks and Vienna’s.