Downgrade to Stock Rom

[2019registered]

Hello,

I am currently using Lineage OS 15.1 but as I have massive lags, I would like to go back to stock rom.
First question:
1) How can I get the offiical rom?
2) What is the proper process of downgrading?

Thanks,

 

[Sutcliffe9]

Just flash this like any other ROM in TWRP. It's the stock 251
https://drive.google.com/file/d/1f3USp3-VncUAtIi2aBzSZ7kzLlYJ7iok/view?usp=drivesdk