To exclude or include an individual field in your document on the fly, first click on the "edit" menu on the right side of the field (the three horizontal dots):

Then select the "Exclude" option. This will deactivate the field. The next time you click the "Populate" button, this field will be removed from the document. Don't worry, you can always navigate to the "Edit" menu once more and select "Include" to include the field in the document once again.