You can also answer in a humorous way, such as, "I can recommend a dentist to you." He may be able to repair your teeth, but your wallet may suffer some damage. " Or, "I can give you some advice, such as being careful when eating sweets and not letting your teeth go on strike again."
Or you can try some exaggerated answers, such as: "I can help you fix your teeth, as long as you can stand me using super glue." Or say, "I can fill your teeth, but you have to promise me not to eat any more sugar."
In short, you can answer this question in a humorous way, but you should also pay attention to respecting the feelings of others. If the other person really needs a filling, it is better to recommend a professional dentist to help him.