Hi @Airpewdiepie,
You can't play PUBG on devices that have lower than 1 GB of RAM (no older devices).
If you want PUBG-type experience on a total 1 GB of RAM (+400MB required free RAM) then you can play Crossfire: Legends, it is by the same group that created PUBG (Tencent Games) but it is required to have internet speed of 4+ MBps and Android 5.1.1 Lollipop or higher.
Good luck.