@Dave529 I hope you are well!
Guests and hosts are under no obligation to review eachother- the guest side review is long, complicated and a lot of guests don't want to take the time- and they certainly don't understand the importance of reviews to hosts when building up their listing and business.
If the 14 day period has expired there is nothing you can do. It's fine to send a message asking your guest to review- but do be aware that airbnb do this to hosts and guests automatically once the stay ends, a few days after and also just before the window closes- so if they did want to they would even without your request.
Best wishes
Paul.