Check for knots first. Then If you notice your string wants to twist up when it goes slack, it’s either gotten too tight or too loose . Imagine throwing sleepers one after another, or practicing Trapeze. Each time you throw, you’re twisting the string a little more in the same direction.
This will help loosen or tighten your string I would NOT attempt if yoyo will not sleep it could snap back and cause injury! use only to maintain string torsion . Take the string off your finger and hold the yoyo and let the string hang down and unwind hope this helps