ccCapt is right that algae will only grow on skeleton, not tissue. But if there is ANY of that SPS
frag that is still alive, frag it down further. Once that algae is established on the bleached skeleton, it'll smother any living coral left on there. It still might be possible to save that coral, but you'll need to figure out why it was dying in the first place.
How long have you had it?
What kind of lighting is it under?
If a recent addition, what kind of lighting was it under before? Could it be light shocked?
What kind of coral is it?
What are the water parameters?