Hi I want to install Plasma OS to my device. It is Huawei Y7 TRTLX1 with 16 GB internal storage and 3 GB RAM. Is it possible to Plasma OS to this device

There is no `Plasma OS`, plasma mobile is a DE. The close thing to `Plasma OS` would be KDE neon. Which is latest KDE on Ubuntu. For your phone, the anwser is no. You'd first have a distro running on your phone and install plasma mobile on it. The easiest distro would be postmarket OS, but they only support to Y3. And Huawei dropped bootloader unlock support in recent years. Which means you can't have anything installed other than the stock ROM.