Promised Ship Date not getting updated during SSD Override

Summary:

Promised Ship Date not getting updated during SSD Override

Content (required):

Wrote an extension to update Promised Ship Date to be same as SSD. First time during submit, it defaults however during SSD override it is not getting updated. Any pointers on how to achieve this?

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):