Use the Lenovo Rescue and Smart Assistant (RSA) tool on your PC to download the official firmware for the TB-8505F.
Tablet will factory reset and reboot. You now have an unlocked bootloader. how to root lenovo tb8505f top
Go to Settings > System > Developer Options and toggle on OEM unlocking and USB debugging . Unlock via PC: Connect your tablet to a PC with ADB/Fastboot installed. Open a terminal and run adb reboot bootloader . Once in fastboot mode, run fastboot flashing unlock . Use the Lenovo Rescue and Smart Assistant (RSA)
adb shell su # (requires existing root – chicken-egg? no) how to root lenovo tb8505f top