That doesn't undervolt. On Linux you 'cannot' undervolt as the userland software doesn't support it, but there's a trick.
Instead you can overclock, which moves the curve to the right (same voltage for a higher frequency), and then add a clock speed limit. You are now running the same frequency at a lower voltage.
Instead you can overclock, which moves the curve to the right (same voltage for a higher frequency), and then add a clock speed limit. You are now running the same frequency at a lower voltage.