You've asked this in a forum about the Intel Fortran compiler. It's not the place to ask about BIOS issues. I'm not aware of a method to disable Hyperthreading other than through your PC's BIOS. Every PC I have used with a processor that supports Hyperthreading has an option to disable it.
You apparently are attempting to modify the Flash while running your O/S.
What you need to do is to enter your system BIOS utility during cold boot.
The way to enter this utility depends on your motherboard manufacturer (some use the Delete key, others something else).
Also, some motherboards have a feature to disable this (enter BIOS setup) the system manufacture (Apple) may disable, but can be reenabled while running the O/S (IOW next cold boot you have a one time chance of entering the BIOS setup utility).
You will have to consult other resources (Google search) to identify how to enter BIOS setup for your motherboard.