You would want to use the Insertfunction and select concat first.
concat(RANK, ",", LASTNAME, "-", STARTDATE) or maybe you do not want the seperating characters but that would be the syntax.
I would probably add a field to your form. Add a rule on submit that sets the field to this formula if it is blank. That way it gets set on the initial submit but not on subsequent where posisbly this data could change. This way you have the filename in your document for future reference.
Then just use this field as the file name in submit connections.
When your form is complete then publish out to SharePoint.