The chain adjustment is located by the door header bracket. It should be a threaded rod that runs through a bent tab. Proper chain sag is @ 1/2" from bottom of rail at max sag point.
This sag is measured by having the system in the fully closed position. On the chain adjustment bracket, loosen the jam nut on the threaded pin that is attached to end of the opener chain while holding the other tensioning nut steady. Adjust tension when loosened, making sure that chain doesn't twist, then retighten jam nut.
I found the threaded rod and tightened the chain to where it was sagging about 1/2" below the bottom of the rail to just above the bottom of the rail. Now when I open the door it still clips the header bracket but continues to open but when I go to close the door it stops as soon as I take my finger off of the down button with a jerk. I push it again and it stops as soon as I take my finger off. etc. I don't think that I fixed it
Improperly mounted header Brackets, spring tension, door/track alignment, sensitivity and force settings may all contribute to the operator not working properly. The entire system may need adjustment. If there is anything further, please ask!!