Forget it. Buy a new one.

Brutal but honest! sometimes its better not to sugar coat things.

I never cared for "Moon Cactus" mutant hybrids, grow the remaining Hylocereus root stock, and throw out the top.

Katlyn.

These mutants are devoid of any chlorophyll and so are dependant on the stock they are grafted onto, for supplying their nutrients.

As above unless you want to try regrafting it.