Normally, Amazon does not allow sellers to use their Small and Light SKUs for MCF.
However, it is possible that Amazon has approved your account for this program. This is not something Listing Mirror can assist in. Amazon will contact you directly about this program to see if you'd be interested.
IF Amazon has given you permission to MCF your Small and Light SKUs, then you will want to enable that in Listing Mirror!
Enabling in Listing Mirror
Go to the edit integrations page for Amazon, click on the advanced tab, and you'll find the option there.
This will prompt LM to send your Small and Light FBA QTY to the other marketplaces for Multi-Channel Fulfillment!