If you aren't skilled in the ways of overclocking your GPU, this GTX 1080 Ti Overclocking Guide at Overclockers Club will set you on the right path.
NVIDIA has locked the GTX 1080 Ti voltage to 1.093v. It does not matter what brand you have, you cannot exceed this without hard modifications to the card. That means your maximum overclock cannot surpass 2.2GHz because of how Boost 3.0 works once again with thermal, power, and voltage limitations.
