I'm looking to create a unique ID for each Form submitted. I'm using SharePoint Online.
The format is ["AN"-YY#####]
First form would look like: AN-1900001
You can activate the Document ID service site collection feature and configure the Document ID setting for static text and format(from site collection settings page >site collection administration >document ID settings)....
If you want to customize this more dynamic way.... you can create another calculated column based on this document id column or can create sample workflow using MS Flow or Nintex.