I think first of all I would approach the guests & ask what happened. Ummm. Why??!! If they actually did that to avoid carrying luggage, I would be shocked & a bit angry. (Take pictures!! You will need them later). If they admit to the car being on the lawn, that is half the battle. ( if their car is muddy, photograph that as well!) I would then explain to them that this is the first time in almost 45 guests that anyone has ever driven over the lawn. I would then say that this type of damage will cost X $ to fix. Then ask them if they would like to pay the landscaper directly or have an amount deducted from their security deposit. Those are the choices. Start the procedure with Airbnb immediately. Get a damage estimate if necessary.
"Yadda yadda yadda. These things happen. I'm so sorry. I wish you had asked me before parking your car on the lawn, next to the sofa & washing machine" (I live in Georgia-- it's more common than you think). "Sorry for the inconvenience, but X$$ is needed to repair the damages. "