To add a rent incentive to a tenant click on the tenant and scroll down to their lease info screen.

Click on their financial tab.

Here you will see their Monthly fees and under that, you can click on the 3-dot menu on the incentives tab: (it has the green text and dollar sign next to it)

From here enter the start and end date for the entire month that they have the incentive for and the discount amount for what they have paid already and push save: