If Intel Extreme Tuning Utility does not let you adjust your multipliers then use ThrottleStop instead. With ThrottleStop you can set your multipliers to whatever you want.
If you want to use the Set Multiplier feature, make sure SpeedStep is enabled and the FIVR - Non Turbo Ratio is set to 0.
To control the multiplier on a 6th or 7th Gen CPU, you should consider using Intel Speed Shift Technology. ThrottleStop lets you access that feature too for full control of the MHz of your CPU.
ThrottleStop also lets you adjust your CPU voltage and a whole lot more. If you do not understand how to set the program up, tell me what you want your CPU to do and post some pictures of how you have ThrottleStop setup.
ThrottleStop 8.48
https://www.techpowerup.com/download/techpowerup-throttlestop/