@Anonymous Welcome to Microsoft Q&A forum and thanks for reaching out here.
I don't think there is a direct migration services as there quite a few differences betwee Dedicated External tables V/s Serverless External tables.
I recommend going through this document to have a better understanding of the difference first and then manually creating the Serverless external tables or by updating the Dedicated SQL pool external table Create scripts to allign with Serverless External tables Create syntax.