If you fish from a boat simply let some line out with nothing but a weight tied to the end, get on your trolling motor and go until you reach the end of the line, then reel back in, pinching the line with your fingers as you reel.
If you fish from shore, find an open area, tie the end of the line to a tree branch, fence post, car, etc and reel in the line while pinching the line with your fingers and walk toward where you tied it off at. When you get to where you tied the line, cut it and the line will twist back to where it should be.