You can see all of your duplicate Amazon FBA and FBM SKUs on the Manage Duplicate Listings page in LM.
Duplicate FBM SKUs
When there are multiple FBM SKUs that point to the same ASIN, they will be linked up as duplicate listings. LM will designate one FBM SKU to be the Primary FBM SKU, typically the first one that imported into LM. But you are able to change this by clicking on 'Make FBM Primary' for the desired SKU. This will be the SKU that LM syncs MF QTY to. The NON-Primary FBM SKU will be handled depending on your Duplicate FBM Strategy.
Duplicate FBA SKUs
When there are multiple FBA SKUs that point to the same ASIN, they will be linked up as duplicate listings. LM will only use the FBA QTY from the Primary FBA SKU. The QTY of the NON-Primary FBA SKU will be ignored. Click 'Make FBA Primary' to change the Primary FBA SKU.
NOTE: The 'Delete From Amazon' button on this page WILL remove the Amazon listing from your Seller Central.