You can update your savings and card payoff goal in the app only during the first 7 days of each month! You will be prompted to set your goal when you open Debbie during the first week of the month.
If you need to make any changes before the week is over you can tap on the pencil icon in the top right corner of the goal screen.
If you miss this window then your goal will default to Debbie's suggestion. But don't worry you can set it again next month!