When I tried put a number like 0,0100 V my bios changed it to "Auto", so I could put 0,0125 V min. or higher number in neg. offset volt. (0,3000 V is max)
By 0,0125 V I have 85% in Power Reporting Dev. I tried 0,05V but I had 80% in PRD during Cinebench.
I should have 100% in Cinebench if I good understood... So I need to put lower number like 0,0100V but that my bios doesn't allow me to do (0,0125 V is the lowest).
By 0,3V it doesn't boot up...

(my specs: R7 3700X, MSI MPG X570 Gaming Edge)
Ok, now I understand what you were trying to say...
But you cannot change the way the motherboard misreport the power by playing with the offset voltage...
The Power Reporting Deviation value needs to be measure at full stock settings, so no manual voltage, no offset voltage, no fixed clocks,... just everything on auto...
What I was trying to explain, was that there is a better way to sqeeuze out more processing power from your 3700x then manually putting x42 and a locked voltage.
So actually nothign to do with the reported 'Power Reporting Deviation', but your 3700x will pull less power and produce less heat if you apply the negative offset...
So from your reply I see that you were able to put 0.05V als negative offset value?
What you should do to find the optimum negative offset value is the following:
1. Take a few base readings with Cinebench R20 with everything on auto. And note down the R20 score, that is your reference...
2. - Go into the bios and put 0.05V as negative offset value (should be a good start) and see if you can find the 'CPU Loadline Calibration Control' and put it on the least agressive setting. With MSI the higher levels are less aggressive, so think you can choose level 8? If your not sure, just leave the CPU Loadline Calibration Control on Auto.
- Boot back into windows, again take a few base readings with Cinebench R20. And note down the R20 score, it should already be better than in 1. with auto settings.
3. Go into the bios and with the +/- sign got a step higher with the negative offset (believe this will then be put 0.0625V?)
- Boot back into windows, again take a few base readings with Cinebench R20. And note down the R20 score, and see if its better than the previous run...
And so on...
The trick is that from a certain (too high) negative offsett voltage your Cinebench R20 results will begin to drop. Then you know you have gone a bit too far with the undervolt.
Go back in the bios and reduced the offset a step or two and your done.
You should then have a much cooler running 3700x, but with high Cinebench scores as it now can boost higher without hitting the thermal and power thresholds...
You can then still further improve your scores by enabling PBO and allowing high number PPT numbers if you desire...