By "nested" I assume 1 part of the 2 part tube is inside the other. Hot water can cause a bit of expansion and act as lubricant. If you have a suitable container (think 4"pvc pipe with cap on one end) submerge it in hot water with dish washing soap.

Yes, one part of the tube is inside the other.

I’m not sure if warm water expansion will make it fit tighter.

I was debating whether to dip it in bucket with hot water or stick it in a freezer.

Maybe attempt to expand outside tube by passing it beneath stream of hot water. Is there a way of hooking inside tube with a piece of wire connected to an imobile object? What I'm thinking is if you find a way of pulling on inside tube while tapping on outside.

I've experienced shop vac tubes so difficult to separate I laid them aside til another day. I suppose that type plastic has a tendency to bind up. I have a couple 5 gallon buckets that have been stuck for months despite random attempts to separate them.

You have the box - so call the manufacturer.