Use this code to change the label on all Submit buttons. This code will override the Submit button text entered in your form Settings.

add_filter('frm_submit_button', 'change_my_submit_button_label', 10, 2);
function change_my_submit_button_label($label, $form){
  $label = 'New Submit Label';//Change this text to the new Submit button label
  return $label;
}