@Momi0 that's not necessarily true - the guest may have a questiont about verification, a technical glitch or other question, that they need answering which isn't directly to do with the listing they have booked.
In answer to the original question. The majority of information the guest needs will be on BNB's website. Personally I find it easier to Google for the information I need rather than using their search function.
Suggest the guest does this first. If they can't find the information they need they can call BNB, use their social media, or raise a query through their website (although I have to admit I am still waiting 10 months later for a query I raised via their site)
Why don't you make a note of the useful guide on contacting BNB at the start of the Community Help forum and the customer contact numbers for each country in case you need them and to pass onto guests.