Anyone have any tips/tricks for loosening string tension on an unresponsive yoyo. UFO works great but it won’t ever come back to your hand as a responsive yoyo would. What i would like to do is loosen the string without killing the yoyo…
Any ideas?
Lots of things you can do. You can bind into a sidewinder for one.
Without binding, hop the yoyo up and push the string out with your non-throw-hand to one side or the other so that your hand is in line with the yoyo, creating a sidewinder-type thing that lasts for a few seconds. You do a few of these hops to adjust tension.
There’s a trick called “washing off” or “washing machine” that adjusts tension.
Let the dead yoyo hang and give it a good spin in the appropriate direction… or taking it off your finger and letting the tension out… these are no-fail methods! 
Probably the best method. Just wanted to add, (I’ll assume you don’t know how to check tension) that to find the right direction to go, check your tension by holding the string close to the yoyo and bring the string you’re holding next to your hand, and sidewind in the direction the string twists.
EDIT: Forgot to add that it has to be a sleeper for my method to work
If I have a lot of tension(which I often do because I’m not much of a slack guy) then I just bind to sidewinder. If it’s just a little I hop the yoyo up from a sleeper and move my hand left or right to do a little mini-sidewinder type thing.
This video breaks down how to deal with it quite nicely in a few different ways