You can set an annual spending decrease rate (% of how much less they will spend each year with the default being 1.0%) under the Retirement Spending Goal, in the Retirement Planner.
Select the 'Pencil' icon next to the spending event to edit the Retirement Spending event. Under 'Spending Decrease', you can adjust the slider bar to the percentage of your choice which will start at age 65 or later (if Retirement age is after 65). Once saved, it will display in your Detailed Cash Flow Table under Retirement Spending, the amount spent each year with the % applied until Zero or when the Spending Minimum is reached.