Hi - just so you know, the SubmitToSharePointList and the companion refresh command are only for use on the Main data source. That means you'd need to copy the SharePoint items into your form's main data source.
So, you could add a repeating group to your main data source and use the CopyTable to copy in the information from the 2DS. Include the IDs, since the refresh command and the submit command will need them in order to know what item you want to delete or update.
Then, after you've copied your items in, running the Refresh command will generate the internal list that Patrick mentions. Allow users to delete, update or add items, and the SubmitToSharePointList command will replicate those changes in your SharePoint list. Hope that helps, please let me know where you could use more info.