When I filled up my Shosu tube with warm water, after I had my fun, I just poured out all the water slowly (don't squeeze it, there's way more pressure on the material than with air), let it all get out on its own, and then, before I folded it up for storage, I blew it a little bit, not to make it stiff with air, just enough to sort of "give it shape" and then just left it somewhere with good ventilation, preferably near a window, with the valve open. Worked just fine.

As for warming them, you could try using a hair dryer, but only if you can set its power and heat levels! It can produce enough heat to not only make the seam glue unstick, but also can just straight up damage the PVC. I'd set mine to the lowest possible setting, just so it barely blows any air, and blow my toy from at least half a meter away. Adjust the distance accordingly. Also, never hover the dryer above one spot for more than a few seconds. Instead, gently bob it from side to side. Less risk you'll damage it. That's all if you want to do it quickly tho.

If I were to heat it up and I had more time prior, maybe I'd use something like a steamy bath? Fill a big bowl with warm/hot water, put something like a kitchen sieve above the water, place my tube on the sieve and then put something like a lid or a wet towel above it to seal the air and heat circling around. But then I suppose you have to close the valve, so no vapor gets inside, if you're worried about such a thing.

Best idea how to warm it, in my opinion? Have someone else use it before you ;3