Have you tried the following?

https://www.dell.com/support/article/us/en/19/sln125793/downgrading-the-system-bios-on-a-dell-system?lang=en

Also this thread...a bit long

https://www.dell.com/community/Laptops-General-Read-Only/Dell-Latitude-E7270-E7470-System-BIOS-1-15-4-Bitlocker-fails/td-p/5082408/page/3

yes i do these steps  but not working

Place a fast spinning table fan directed at laptop's bottom air intake vents  while gaming and then games run at constant 60 fps, ex: gears 5