Hello @Carol29,
Try explaing your situation to the guest and ask them to send a re-request after you have updated the prices. Hopefully they should understand. Tell them that you are declining the current request.
Also, a lesson to learn, always keep your calendar updated 🙂
I had a guest request for christmas last year in August and I was lucky that the guest understood that the calendar wasn't updated and obliged to pay the higher price.
I hope it works out for you 🙂
Jeet