add_filter( 'frm_fields_for_csv_export', 'remove_specific_field_from_csv_export', 10, 2 );
function remove_specific_field_from_csv_export( $fields, $args ) {
	$target_form_id = 220; // change 220 to the ID of the form
	if ( $target_form_id === (int) $args['form']->id ) {
		$target_field_id = 1204; // change 1204 to the ID of the field to be removed
		foreach ( $fields as $key => $field ) {
			if ( $target_field_id === (int) $field->id ) {
				unset( $fields[ $key ] );
				break;
			}
		}
	}
	return $fields;
}