You could try to import BDC Model in bcs to create external content types: https://learn.microsoft.com/en-us/sharepoint/manage-business-connectivity-service-applications
And here is a third party tool BCS Meta man to build BDC Model file, hope it's helpfu to you.
Third-party information disclaimer:
The third-party product that this article discusses is manufactured by a company that is independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of third-party products referenced in this article.
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