Only the QuickBooks Administrator can do this.
To do this task
Choose Edit > Preferences.
Click the Bills icon and click the Company Preferences tab.
To automatically apply existing vendor credits when paying bills, select Automatically use credits.
To automatically apply early or on-time payment discounts when paying bills, select Automatically use discounts.
Select a Default Discount Account for tracking applied discounts and credits on your profit and loss statement.
Click the OK button.
As you select and highlight each bill,
the amount of any discount or credits is automatically deducted
from the Amt. to Pay for that bill.