isn't it already unlocked??
are you using msi afterburner ??
if so make sure that you have checked the box inside settings that say "unlock voltage control"
Sorry i don't have the card already but i saw in all the online reviews that this card have the voltage locked at 1.2v and for this reason i' m looking evrywere to find a way to unlock it (i read somwere that the way is flash a modded bios)
This card have so many overclock potential but for some reason sapphire had lock the voltage