You can merge your listings on the Product level. This is not the same as merging marketplace listings, which consolidates the listings on the marketplace
When you create new listings thru Listing Mirror, Listing Mirror uses your product to determine the variation grouping on the marketplace. So if SKUs A, B, and C are variants of the same product, then they will be grouped as such when created on a marketplace.
In order to merge listings, go to the Product page for the LMSKU (previously called Master SKU) you want to keep, locate the Actions dropdown menu, and select Merge Listings.
After you've clicked Merge Listings, a pop-up will be displayed asking you to "select the parent listing to merge with."
To do this, click the dropdown widget and enter either the sku, variation title, or title of the parent listing you would like to merge with. Once you've identified the parent listing you want to merge with, select it from the dropdown widget and click Merge.
In the above example, I merged SKU bisselA with SKU bisselB.
Once the merge has completed, you can scroll down to the Variants section of the Product page and you should see all of the listings that were originally with this parent listing in addition to the listings that were merged.