@Melissa595 Use the guest's Airbnb email address to send them an email. Go to message the guest, as you usually would through the Airbnb messaging feature on your desktop pr laptop. On the left side of the screen, way at the bottom, under About this guest, there will be a temporary email address.
It will look something like this:
melissa-sasf73389rq8934r89r@guest.airbnb.com
Just send them an email to that address, and include your real email address in the text. Have them email you directly from their personal email address to that address (i.e. not just replying to the message).
Hope this helps!