I think you could do this with function calling. You could set up a custom function called checkAddress. The LLM can then send their address to a custom server where you handle the logic and see if their address is valid. At the end of this logic you can send a response saying " invalid address, ask again." or "valid address". I think this way would be more accurate than just feeding it a knowledge base and telling it to find a match, however It could be worth testing as the knowledge base route would be quicker and easier to implement