Here are some steps to repair a damaged flue cap:

1. Inspect the flue cap: Before repairing the flue cap, inspect it thoroughly to determine the extent of the damage. If the damage is minor, you may be able to repair it yourself. However, if the damage is extensive, it's best to call a professional chimney sweep to handle the repair.
2. Clean the flue cap: If the flue cap is dirty, use a stiff brush or wire brush to clean it thoroughly. This will help remove any debris or soot buildup that may prevent the cap from functioning properly.
3. Replace damaged parts: If any parts of the flue cap are damaged, such as the screen or cover, remove and replace them with new parts. Be sure to use high-quality replacement parts that are designed for your specific flue cap.
4. Secure the flue cap: Once you've repaired any damaged parts, make sure the flue cap is securely fastened to the chimney. Use screws or brackets to secure it in place, and check to make sure it's level and properly aligned.
5. Test the flue cap: After repairing the flue cap, test it to make sure it's functioning properly. Look for any signs of damage, such as cracks or gaps, and make any necessary repairs.

Repairing a harmed flue cap entails cleaning up the cap and checking, changing any damaged parts, securing the cap to the chimney, and testing it to ensure it's working properly. If you're not sure about how to fix your flue cap, it's constantly best to call a professional smokeshaft sweep to manage the repair work.