This restaurant complaint reply is perfect for when the owner wants to be apologetic and accommodating to the customer.
Dear ____________________,
I would like to extend my deepest apologies for your experience at my restaurant last night. As head chef, I want nothing more than to ensure that birthdays, anniversaries, and other events are the best they can possibly be. All of us here are committed to top-quality food and dining experiences.
Had I known of the issue with your meal at the time, I would have taken action immediately. Since it's too late to comp last night's dinner, please accept my personal invitation to return and dine with your party on the house.
Please reach out to me and let me know when you plan on joining us. Again, I am so terribly sorry that we didn't meet your expectations and hope you will give us the opportunity to correct it.