1. Find a rope or belt: If there is no other substitute, you can find a rope or leather belt instead of a belt. Tie the rope or belt to the trousers loop, and then tie it.

2. Use pins or staples: If you happen to have pins or staples at hand, you can try to fix them at both ends of the waistband and nail the waistband to the trousers loop.

3. Ask others for help: If you have classmates or instructors around you, you can ask them for help and see if there are any extra belts you can borrow.

4. Repair with sewing tools: If you have sewing tools, you can sew the waistband again. If you are not familiar with the sewing operation, you can try to find someone who knows how to sew to help repair it.

5. Buy a new waistband: If the above methods can't solve the problem, the easiest way is to buy a new waistband to replace the broken waistband. It can be purchased in shopping malls, supermarkets or online shopping platforms.