Found on the interweb
"If the combination was somehow changed, try shining a flashlight into the spaces where the thumbwheels turn. As you rotate the wheel, you'll see a small notch once it gets to the correct number. Line up all three thumbwheels in this way, and it should open.
You can also use a thin strip of metal if you have trouble using the flashlight method. Using a thin strip of metal – (we suggest one cut carefully from an aluminum can) - to insert into the space beside each thumbwheel - hold pressure on the metal strip as you rotate the wheel - you'll feel the notch as you rotate - stop when you feel the notch and move on to the next wheel until you have all three set."