No operative System and twrp recently i installed a custom rom on my phone, then i decided to expand my phone memory on a trick i saw on youtube, where i had to go into twrp, unfortunately i clicked on delete system. afterwise when i then tried to boot my phone it was stucked on the logo screen and somehow the twrp is replaced with the android one, when try to open the recovery mode. I was wondering if there's any possible ways to fix this?

EDIT: Curently i'm using a chinese phone called "Cubot S308"
The obvious solution to having no operating system is to add one. That's why what you can do, is to re-flash the custom ROM you are having, or a different one (maybe even a stock ROM). You can go on their page, and find your build there.

Once you download the ZIP, you put it on your SD, through the computer, and flash the ZIP from there, or you can use ADB to transfer the ZIP and flash.