When dealing with a damaged mirror, your approach will depend on the extent and nature of the damage. If it’s a minor scratch, you can attempt the following DIY methods:
Toothpaste: Apply a non-gel toothpaste to the scratched area using a soft cloth and gently buff the scratch with small, circular motions. Clean the area afterward with a damp cloth.
Baking Soda Paste: Combine baking soda with water to form a thick paste. Apply it similarly to toothpaste and buff gently.
Mustard and Vinegar: Mix dry mustard with white vinegar to form a paste. Apply this mixture to the scratch, let it sit for a few minutes, and then wipe clean.

For cracks or more significant damage, consider the following:
Repair Kits: Purchase a glass repair kit, commonly used for windshield repairs, that might work on mirrors as well. Follow the instructions provided in the kit carefully.
Professional Repair: If you’re unsure about repairing it yourself or if the damage is extensive, contacting a professional glass repair service may be the best solution to restore the mirror effectively.
Replace the Mirror: If the damage compromises both appearance and safety, it might be more cost-effective to replace the mirror entirely, especially if it’s an integral part of a bathroom or vanity setup.

In any sign of deep cracks or severe breaks, avoiding the use of the mirror altogether until it’s repaired or replaced is advisable, as it can pose a safety hazard. Always wear gloves and use caution to prevent injuries when handling broken glass.