Get someone to stand outside the pool where the pipe goes into the pool for the return you want to try to turn. Have them hold that pipe so there is not chance of it moving. Then YOU turn to turn the outer ring of the return in side the pool. There should be bumps to help you hold it. Turn it COUNTER clock wish aka towards the LEFT......remember Righty-Tighty, Lefty-loosy.
If you hands cannot grip it then you can try a "strap belt" like this:
2 Pc Rubber Strap Wrench Set make sure to have it ONLY on the bumpy part of the ring.
Now if that does not work you can VERY CAREFULLY use a flat head screw driver and hammer. You will put the blade inside one of the areas between the bumps and GENTLY tape the hammer on the handle end of the screwdriver. If it does not give with that STOP and don't mess with it any more. We do NOT want you to break the pipe
I only have one return but I also have a round pool so it works fine with one. With your pool be an oval it might need two returns to make it move like it should to use your weir doored skimmer (Good learn on your part!)
Now lets go a step further on trying to get you a fountain to help cool your pool off. Is your equipment hard piped? As in does it have PVC pipes running from the filter/pump to the pool? I have an idea but need this answer first.
Kim