Fit the rubber band into the groove on the motor, and above the groove around the LDS.

Push the rubber band down, then rotate the LDS to drive the rubber band into the groove.

Do a full rotation and seat the entire rubber band.

Give the LDS a test spin. If it spins freely and comes to a slow stop, it's good. If it stops abruptly, you applied it wrong or something else is seizing the motor.