This is an extremely generic question. I don't know exactly what you are trying to achieve here.
So the answer can only be generic.
From the Unity side, all you have to do is assign host access to the LUN. Add new host and remove the old. But depending on OS/host type, this may drop access during transition.
What kind of host is this?
If ESXi, for example, simply give the LUN host access to the new host and then use vmotion to reallocate host side resources before removing the "old" host.
Again, this is a very generic question. If you need more detailed feedback, please be more specific.
Andre @ Dell EMC