@Ashlee129
There is no promotional "code" or similar.
Other options:
1. If the guest in future sends you an inquiry ("contact host" link on the listing), then you wll be able to sent a special offer.
2. If the guest announces by message the desired dates upfront, then you can adjust the prices for that dates (guest must book immediatelly after the adjustment)
3. If the guest makes a booking as useally, then you can use the "change" option on the reservation to adjust the price.
Option 1 is the preferred one: ask the guest to sent an inquiry if he/she wants to book again in future, so you willl be able to sent a special offer.