Hi Michael David! Thanks for your question!
If the birthplace is not on the document, then you would mark the field blank using Ctrl + B (PC), Cmd + B (Mac) or the x icon on a tablet. Tip: This kind of information is found in the Field Helps. Clicking on the question mark that shows up when you click on a field displays the Field Helps. The field helps give a lot more help in addition to the Project Instructions and examples.