pocketmine\event\block\SignChangeEvent::setLine PHP Method

    public function setLine($index, $line)
    {
        $this->lines[$index] = $line;
    }

 public function signchange(SignChangeEvent $event)
 {
     $event->setLine(0, "sJimin's");
     $event->setLine(1, "First");
     $event->setLine(2, "Plugin");
     $event->setLine(3, "work!");
 }