You cannot simply add more copies of voting disks to increase redundancy because the number of voting disks is managed by Oracle ASM and determined by the redundancy of the disk group.
To increase the number of voting disks, you need to move them to a disk group with higher redundancy.
So, create the new disk group or identify one that meets your requirements and use the:
crsctl replace votedisk command to move your voting disks to the new disk group.
