add_action( 'user_register', 'auto_assignrole' );
function auto_assignrole( $user_id ) {

$userstudent = get_user_meta($user_id, 'student_id', true);
$usercompany = get_user_meta($user_id, 'company_name', true);

if($userstudent != '' || $usercompany != ''){
   $user_id = wp_update_user( array( 'ID' => $user_id, 'role' => 'Student' ) );}
}