Hi @Lorraine471 ,
I myself have never done an extra day promotion though I think you can customize your own promotions. Menu> calendar> setting button at right top>pricing, scrolling down you will find Promotions>choose date and set a discount.
There is also a coupon offering too where you can give them a special offer but only if the they have not booked already or you can still give them a discount by changing the reservation details.
I did this once but was in close communication with the guest to book as soon as I marked my price down as if it's an open booking first come first served.
I hope this help you somewhat. I am new to this promotion/discount as well.
Bettye6