Instructions
Remove the old yo-yo string. Many manufacturers use twisted strings (just like modern replacement strings). Look carefully at the yo-yo string and note how the two strands twist around each other. Holding the string tightly very close to, but not touching, the body of the yo-yo, rotate the yo-yo counter to the twist of the string to unwind it. This will open up a loop in the string, which you can either cut and then pull one of the single strands until the rest of the string comes off the axle or loop over the outside of the yo-yo until it comes off and pulls over the body.
Grasp the unknotted end of a replacement yo-yo string. Twist it counter to the way the strands wrap around each other to open a loop, stick your fingers in and widen the loop from the inside until it is large enough to pass over the outside of the yo-yo.
Slip the yo-yo string over the body of the yo-yo and between the two halves. Release the yo-yo and allow the string to retwist itself until the loop is sealed and tight around the axle.
Measure the yo-yo string by placing the yo-yo on the ground by your feet with the string fully extended. Cut the strings at a length 3 inches above your waist and tie a knot in the end. This should allow the string to be the length of your waist to the ground when around your finger during play.
Wind the yo-yo. Hold the yo-yo in your left hand, index finger outstretched, and wrap the string around both yo-yo and finger until you bring the string all the way around to where you started. Wrap around again but this time do not wrap around your finger. Release the loop around your finger and wrap the yo-yo normally, allowing the loop to be pulled between the yo-yo halves as you go.
Tie a slip knot in the knotted end of the yo-yo cord for your finger, and the yo-yo is ready for play.