Open your lock with the existing combination. Turn the dials left-to-right or top-to-bottom until your combination lines up with the white markers on the lock case.
Hold down the "Reset" button on the side of the lock beside the TSA keyhole. Look inside the base of the lock if there is no reset button. Hold down the small metal bar in the middle of the lock with a pen or pencil.
Spin the dials with the "Reset" button or bar held down. Line up the digits of your new combination as you would when you open the lock. Release the "Reset" button and jumble the dials. The new code is set.