Are you using 64GB x 2 in your system?
According to the manual, the mobo supports only 32GB DRAM stick. In order to get 128GB, you need to install 32GB x 4 on the mobo.
If you are using 32GB x 4, then double check whether you have inserted the DRAM sticks into the socket securely.
At this point, there is no need for you to tweak the voltage until your mobo recognize the correct DRAM capacity.
Please check the manual of your mobo.