Most modern yo-yos have a transaxle or ball bearing to assist this, but if it is a fixed axle yo-yo, the tension must be loose enough to allow this.
The two main ways to do this are, allow the yo-yo to sit at the bottom of the string to unwind, or perform lariat or UFO to loosen the tension. When one decides to end the "sleeping" state, one merely jerks the wrist and the yo-yo "catches" the string and rolls back up to the hand. Ball-bearing yo-yos with a "butterfly" shape, primarily used for string tricks, frequently have low response or are completely unresponsive, requiring a "bind" for the yo-yo to return".