If you have products in separate product groups that should be in the same product group, you can use the bulk update tool to combine them. Since products are grouped together by Variation Grouping ID, the ID can be changed (or added) in order to put products in the same group.
1. Export your catalog on the Bulk Upload page by clicking on the button marked "Full Catalog". The file may take a few minutes to export.
2. Click on the green cloud icon in the Status column to download your file.
3. Open the downloaded file in Excel.
4. Find the products that you would like to group together using search or filters. Find the Variation Grouping ID field for all products and change (or add) them so that they are the same.
NOTE: Make sure that the Variation Grouping ID is not taken by any other product group, or those product will go into the incorrect product group.
Be sure that all fields listed are the same for every product in the group.
5. After you have made your changes, save the file (as a .csv) and re-upload your catalog using the Bulk Upload tool.
Contracted and/or Featured product groups must be ended in order to add/remove products. Please work with your buyer to end and re-contract & re-feature before changing the variation grouping ID in bulk.