Loosen wing lock. Turn valve CCW to relieve pressure. Broken a few due to being obscenely tightened.
If you relieve tank pressure, and remove the hand wheel, you can remove the whole valve and work it off the machine (in a vise, etc.).
BUT, being that it is a tensioner valve, use due care in removing...ie, deep socket with extension and rag stuffed into the frame hole. Technically, the pressure and excess oil will go back to tank when removing, but, again, I've seen weirder.
Oil loss will be minimal.
Track tension is derived from rabbit travel pilot pressure....so, upon reassembly, place machine travel in rabbit and tip the travel lever (either one) into travel (either direction).