Best way to make a support chatbot

In short, I have a file with all questions and answers to which I want the chatbot to answer. In all other situations which are not questions (or questions similar to) the ones provided in the file (which can be in any format, but is currently jsonl for fine-tuning) , I want the chatbot to answer with something like “I am only here to answer questions about topic X or Y, not any other topics, please try again”

What is the best way to achieve this behavior and how ? Embedding/Fine-tuning ? What will I need ?