Honestly, as old as that looks, I’d be replacing the regulator amd the hose. The part doesn’t cost that much.
PD blaster is better than WD40 for things like this. If you have WD40 try it. Soak it. Leave for 10 minutes and soak again. Then try.
Right tight, left loose.
You should be liberal with WD-40 before trying again
I’d have a good look at that hose, somebody wrapped it in tape for a reason.
Give it a really good going over with a wire brush so that the metal and threads are exposed. Get some PB Blaster (NOT WD-40) and give it really good soaking. Then tap it gently with a hammer for a minute, then give it another good shot of PB Blaster. Go off for a long coffee break and try it again. The fitting on the bottom looks likes part of the regulator, and the top is the hose fitting. You want a proper fitting wrench on both fittings.
Counter clockwise to loosen.
Quite possibly left hand thread, try tightening it instead.