I am suprised that posters here are trying to advise you how to circumvent the system BNB has set up to protect hosts.
BNB doesn't allow hosts to provide contact details to potential guests (or visa versa) before a booking is confirmed. This is to protect you as a host (as well as BNB ensuring it gets its money).
There is a security risk in guests having your contact details in advance of booking. And many guests who want your details often want this to try and circumvent using BNB and/or ask for a discount, which of course means, you wouldn't be protected is something goes wrong
Your guest should be able to get all the information they need from your listing and by talking to you via messaging on BNB's site.
There are other listing company's that enable you to chat to guests in advance of booking, if that is your preference.