Hi, welcome aboard
Don't worry about losing argon or nitrogen.. first off, you won't lose any by just turning the objective lens and secondly I wouldn't lose any sleep about not having any in there in the first place.
To reparallax a bushy 10x40 you'll need a rubber strap wrench to loosen the objective ring.
Set up the fast focus ring first so that the crosshairs are crisp.
Once you've loosened that turn the objective lens until both the crosshair and the target are in sharp focus and you can make out fine detail on the target - screw threads, fine blades of grass etc. Once you've got that, it's parallaxed for 23 yards. Don't just turn the objective lens a prescribed amount such as 1/4 of a turn or 1mm.. it needs to be set for your individual scope and for your eye.
Once you've set the parallax, you'll need to lock it in place. What I do is put some black electrical tape round the gap and then hide the electrical tape by fitting a butler creek flip up over it.
You might find my article on scope setup an interesting read
There are some other articles on the website you might also find useful.