Content Matrix scope is limited to only items migration but before that we should follow Prerequisites for Migrating BCS and BDC Data as documented
https://support.quest.com/technical-documents/metalogix-content-matrix/9.3/sharepoint-edition-user-guide/21#TOPIC-1590025
Steps we should do before we migrate items from external list using Content Matrix:
Setup "external content type" in target SPD that should match with content type and pre-create external list in target SharePoint site