Hey, thanks for your reply.
I followed the official documentaion, that’s why. apt-get update are included laso in the documentation as you suggested but still no luck.
https://docs.graylog.org/en/3.3/pages/installation/operating_system_packages.html#operating-package-upgrade-deb-apt
wget https://packages.graylog2.org/repo/packages/graylog-3.3-repository_latest.deb
sudo dpkg -i graylog-3.3-repository_latest.deb
sudo apt-get update
sudo apt-get install graylog-server