To create a Custom Group, go to Products Catalog->Custom group tab.

Then, expand the appropriate group listing and click on the + sign to add a new group.  

Name the group and click the checkmark to confirm. Be sure to click SAVE when finished.

The final step is to assign the custom group to items.

First, refresh the FULL WEB BROWSER for Prime to update the group and make it available to select on other pages.

Once you refresh, the Products Catalog search screen will display. Search for the items that need to be added to the group. Ex: Gatorade

Then, select the items and click BATCH EDIT ATTRIBUTES from the action button:

Click in the Custom Group field to assign the appropriate custom group name. Then confirm items selected and click ok to assign.

Then