Hi. I'm a host and a future guest wants to increase numbers before their arrival next week. How do they do this via the Airbnb booking system.. Thanks Nige
If you mean increase the number of guests, Timothy (Nigel), they must request to change the reservation. They should have such a button in their panel.
If you are happy for them to do this, tell them to go into their booking confirmation, hit the amend button and add the extra person. You get a request to accept. You accept.
Job done.
Have a look at the Airbnb Help Centre it answers this and lots of other FAQs
I generally find it is easier for me (the host) to initiate the change, and then they confirm it. It seems a lot of guests don't know how to do it (most changes are for extra nights after check, or when they incorrectly list the number of guests).