How to add a placeholder to the drop-down menu in the contact form 7

Trying to find a way to add placeholder in the contact dropdown form 7, I tried first_as_label, for example ([select company-size first_as_label “Company Size” “1-10” “11-50” “51-100” “101-500” “501-1000” “1001-5000” “5001+”]
)

But it did not work, can anyone help please?