What material is it?
While this iss not recommented, when I had to replace a sprinkler valve (threaded ports), I cut through it and unscrewed each side separately. I installed male adapters on the new valve and just put a big glob of cement on the old male adapters and set the new valve down.
In other words, glude an smooth bore onto a threaded pipe end.
If the materials are compatible, and the pipe size is snug enough, just glue it.
If that squigs you out - try a flex connector - a rubber cylinder with SS screw-down straps on each end. Again, either get a close size pipe, or - real plumbing supply stores carry adapter-type connectors - one end is one diameter, the other another.
I do hope you plan on burying the pipe and bringing it up IMMEDIATELY next to the pool - I fear what will happen if someone bumps a pipe connected to a soft, flexible pool liner.
Can you install a ridged panel to the frame, and put the connectors through that panel?