Do you know the exact nature of the complaint?
Honest, constructive, criticism is a gift. I’d rather have a client complain and then have the opportunity to consider their feedback than a client stop coming or have a defensive relationship with me but not tell me why.
After you know the exact issue, you can decide whether it’s something you can change, and if it’s something you’re willing to change. There are some aspects of my teaching persona that are non-negotiable, even though I could change them. They’re what make me, me. Don'[t be afraid to be who you are and refer clients to others where necessary.