If you made a mistake while checking an item, you can use the search function to make changes to items that have been checked previously.

For instruction son how to search for an item, check here: How do I access items not in my list of items?

Once you have pulled up the item in Date Check Pro, you will either get a screen that shows that there is no active inventory in the program or one that lists where the item is located in the store.  Examples of both are shown below:

Based on the change that you need to make and the current status of each particular item, you will find a variety of buttons on the bottom menu that should give you the option that you are looking for to update the item.  If you are looking to correct the date of the item if it is incorrect, you can click on the item as shown below and follow the prompts to type in a new date.