Asus India — mobile lag while playing games

Address: Vijayawada, 520008

Serial no: k1aagf0259642n5

I had updated my asus zenfone max pro m2 to android pie after official announcement by asus. Immediately after the update was completed, screen was started flickering... I browse the internet for solution, but negative.
Finally, i gone through the asus service care in vijayawada, krishna-520008, andhra pradesh, india. They degraded my firmware to android oreo and given me.

Now i am facing the "lag issue..." while playing games and bruising internet.

Please, checkout this problem and give me a better solution.

Gmail id : [protected]@gmail.com