I haven't found many things related to the use of the Morph Brush in R3F and Nvil.

So this is my understanding on how it works.
I think these tools can only be accessed with a Rocket3F Pro license.

Let's start where we stopped in the "Missing Tutorials Part1" with a head that's been deformed using the FFD Lattice technique.
This will be our Morph Target object.
For the Morph Brush to work we also need a Morph Source object on which we will apply morph deformation.
This will be the original head used at the beginning of Part1 tutorial.
Here it is hidden.

I have made myself a "Deform" button that I can use either for morphing purpose (like in this tutorial) or for UV Deform (that will be described in another tutorial).
It is mainly here to remind me how things work as I didn't find any way to create a button for the 1st step.
So the only thing it does is to open the Sculpt window after the 1st step has been done manually.

The 1st thing to do is to align our Source and Target objects in all views.

Then we have to set our Morph Target object. This can only be done in the Scene Hierarchy window and I couldn't find a way to create a button for this action.

You can now hide the Morph Target object (recommended).

And launch the Sculpt window to start painting the original head with the Morph Brush.

Once you have finished you can continue with the classic modeling tools if you want.