Here are some steps you can follow to resolve a customer complaint at a restaurant:

1. Listen actively: Let the customer fully express their concerns and show that you are paying attention.

2. Apologize: Express regret for the inconvenience the customer has experienced, even if it wasn't your fault.

3. Take responsibility: If the issue is within your control, offer to make it right. If not, explain the situation and offer a solution where possible.

4. Offer compensation: If appropriate, offer a discount, coupon, or other form of compensation to show that you value their business.

5. Follow up: Check in with the customer after the issue has been resolved to ensure their satisfaction.

6. Learn from the experience: Use the feedback to improve your processes and prevent similar issues in the future.

Remember, the key to resolving customer complaints is to be empathetic, solution-focused, and to act quickly to address the issue.