Short of getting one, a piece of pvc plumbing tube and a hack saw, a pencil would help too if DIY is your thing. It's a bit like those keys to open the back of your watch, annoying when you dont have one or if you want to open your old nintendo game cart!
I think Naish and F-One wings use same type of valve as do SUPs so maybe appeal to locals to borrow one. If hole is same side of valve as zipper you can pull just that part out and fix.
8.99 usd on amazon - about as easy as it gets these days Halkey Roberts Valve Wrench 6 Section Screw Air Valve Wrench 6-Groove Spanner 6 Hole Valve for Inflatable Boat Raft Dinghy Kayak Canoe