How to tighten the belts?
Loosen the screw on the synchromesh gear which drives the corresponding belt you want to tighten.
Hold the belt’s end reaching out from the black sliding block with a clamp.
Loosen the screws on the sliding block with the L-shape wrench, then use a clamp to tighten the belt properly. Finally, lock the screws back on sliding block and synchromesh gear.