To reset a price back to the price setup in the product setup, you will need to click on the Reset price button in the upper left area of the Maintain Order screen.

If you are logged in as an authorized user to reset the price, it will simply reset the price back to the stock price for that line item. If you are not authorized, it will pop up a security window asking for a user/password of someone authorized to reset a price.

Once the price is reset you will notice the red asterisk to the right of the price will disappear indicating the stock price is displayed.