The blank option appears because the default value for the field is an empty
string. If you set the default value for the field to one of the values
listed in the dropdown, the blank option will no longer appear.

If you want "Select..." or some other string to appear when the field is
empty, your XML file will need to provide both a value and a description for
each repeating element. You can then add an element to the top of the XML
file that has a blank value and a description of "Select...".