@Anna11257 You could certainly ask Airbnb to call the guest on your behalf, letting them know you found their device and to check their messages, as you have sent them one.
You actually should have a place off-platform where you keep a list of guest's phone numbers and email addresses, if they have given them to you. Write them down as soon as a booking is confirmed. (As more of a pen and paper gal than computer-oriented, I have a little book I use for this)
It can come in handy for all sorts of things. You might want to contact prior guests to let them know about a new listing you have, or renos you've done, or a special promotion you are running.
And most importantly, if there is a tech glitch or Airbnb should suspend your listing for any reason, you will still be able to contact guests with upcoming reservations.