I usually drag them in by my kite leash to their harness hook. The person being rescued just needs to flag their kite. Its not super fast and sometimes you need to constantly loop you kite in lighter winds. I recommend most people dont wind up their lines in the water. If you screw it up its super dangerous and could make thinks worse. Just flag it and drag it. You shouldn't be out further than you can swim, and winds shouldn’t be offshore right?
When i do lessons i carry an extra handlepass leash on my harness to tow with or attach to a board so i can carry it over my shoulder.
If kiters are playing by the rules the wind will take them back. If not, they made some bad choices and need help.
Last time i had to rescue someone it was my girlfriend. She bridle wrapped her shity LF kite and was drifting out to sea at Silver Sands in Barbados I felt bad so i helped her instead of making her swim for it. I am such a nice guy.