Check out Manage a variant group to learn how to edit your groups.  

Your groups will merge to appear on the same page. While you can group, modify and delete your own variant groups, any items in other groups will continue to appear on the item page. Consequently, you may not always be able to define which content will be displayed on a product page if there are multiple sellers providing content for the same item. Walmart will determine the best available content for items unless provided by a brand owner or authorized reseller. 

You can’t create custom variant attributes. Choosing the correct product type is important because variant attribute names are populated based on the product type of the items in the group. Check to see if there’s another way you could set up your item using a supported variant name. For example, if you’re selling vitamins in one-, two- and three-bottle packs, you could set them up to vary by count  instead of by bottle. If you’re unable to find an alternative like this, you shouldn't set up your items in a variant group.  

Every subcategory or item type has a ranked list of variant attributes that defines how the attributes show up on the item page. For example, clothing items will always list the item’s size first followed by the color.  

That depends on the variant. For a single variant item, there's a limit of 50-100 variants—for example, a towel that comes in 100 different colors. For a multi-variant item, there’s a limit of 1,000 variants—for example, pants with 25 different sizes and 20 color options.  

If the primary variant goes out of stock, the grouping remains valid, with the primary variant showing as out of stock on the item page. If you decide to discontinue the primary variant (e.g., never add inventory again), you have the option to set a different variant as the primary by updating the variant group list with a different primary item selected. If your item is in a merged variant group and the other seller's primary variant is out of stock, select the Help button in the Seller Center menu bar to contact Support. 

The Walmart variant group takes precedence. Your items will be included under Walmart's group if all the items match the items in that group. Matching is done using the item's unique item ID (e.g., UPC, ISBN). If you decide to discontinue the primary variant (by never adding inventory again), you have the option to set a different variant as the primary by updating the variant group ID grouping with a different primary variant selected.