Power down the treadmill and unplug it from the wall. Inspect the belt for excessive wear and replace if necessary. Deep grooves in the belt indicate extensive damage and that the belt is at risk of stretching.
Locate the belt adjustment bolts on the rear end of the treadmill, on either side of the belt. Loosen the bolts on both sides with the Allen wrench, turning the bolts 6 to 8 times counterclockwise on both ends. Pull the belt with your hand to check for looseness. When you can lift the belt 3 inches away from the walkway on either side, it is loose enough to lubricate.
Lift the belt and squirt half the tube in a zigzag pattern beneath the belt. Then lift the other side of the belt and squeeze out the remaining lubricant in a zigzag pattern. The manufacturer usually supplies enough lube in a bottle or tube for one application.
Tighten the bolts clockwise the same number of turns on each side as they were loosened. If the belt does not self-adjust as it should, you may need to loosen or tighten one of the belt bolts individually until the belt slips back into alignment. You will have to experiment until you find the proper alignment.
Plug the treadmill in and let it run for three minutes. Then walk on it for another three minutes so the lubrication spreads across the walking deck beneath the belt. Wipe away any excess lubricant that comes out from beneath the belt with a damp cloth.