Hello @Laurie-and-Erik0,
Go to your reservations and find the guest to whom you wish to sent the lease.
Click on the "Contact by email" link in their reservation and send them an email as you would usually send one.
The "to" address will look strange as it's an anonimised email address, used to keep the guest's real address private.
The article below outlines the idea.
how-will-my-email-address-look-to-other-people?
Airbnb doesn't chollect the "security deposit" in advance so there's nothing to refund. It's just an amount up to which Airbnb may charge the guest if the host makes a claim that's upheld by Airbnb.
The article below explains what they mean by the term "security deposit".
How does Airbnb handle security deposits?
Steve.