1) remove all corals to a bucket of seawater.
2) remove all liverock to a bucket of seawater.
3) using a small pail and a herding device, herd fishy into the pail and remove to a waiting bucket of seawater. Try to avoid using a net.
4) replace all liverock and corals.
5) return fishy to LFS or to a different tank in your system.
It is a pain in the neck removing a fish from your tank. Good luck.