This Sitecore Submit Action is provided by a default S4D installation, and allows adding an S4D recognized identifier to the current Sitecore xDB Contact.
This Submit Action must precede any Save to Dynamics Submit Action if you wish for the S4D facet to be saved against the Contact, which includes information on the Dynamics 365 entity created or updated.
A form field must be selected to Identify Sitecore Contact by, typically this would be an email address but allows any valid field that you wish to use as an identifier. The value of this field will be saved as the S4D identifier, unless empty.
The Submit Action also offers optional functionality to save built-in Sitecore preferred Email and Personal Information facet values from form fields if you wish.
Contact identification requires the Sitecore Tracker to be running.
Testing and development
S4D includes significant debug logging output to help troubleshoot any problems.