Menu option is Settings > Object Tracking > Object Types > Custom Information. Select the appropriate View Type. Click to highlight the category and click Items. Click on an Item and click Data Codes. This only applies if ‘Has Data Codes’ is checked for the Item.

Data codes are the valid entries for selection within this item. 

Each Data code has a description assigned to it. The data codes are the valid entries for a selected item and will show in a picklist if the search button is pressed when a data column is selected.