Loading a Real Time Operating System into the Amazon DeepRacer

Hi, I am wondering if it is possible to load an Real Time Operating System into the Amazon DeepRacer. However, the OS cannot be booted up due to security issues. The message was displayed on the external monitor connected to DeepRacer. Specifically, I followed the instructions from here. https://docs.aws.amazon.com/deepracer/latest/developerguide/deepracer-vehicle-factory-reset-instructions.html Usually, there is an option to disable secure boot in the BIOS setup, but I can not find it.