The process of setting control from points in a point cloud is generally the same as setting individual control points. However, when a point mesh is imported for control, the point cloud will typically be quite dense:
To facilitate the assignment of individual points in the point cloud as control the above view will appear, and you need to select and create individual key points from the point cloud. First select a point in the point cloud that corresponds as closely as possible to a 3D point in your project (you may need to zoom in), then click the "Create Control" button at top. Each time you do this the point will enlarge in the viewer and its coordinates will be added to the table below the viewer:
When assigning the point to an existing 3D point in your project, use the selected point in the table and follow the typical assignment process. See Marking/Pinning Multipoint Transform, Control and Pinned Import Points for information on marking and assigning control points.
You can create the control point and assign it at once by pressing the Assign button while a 3D point in your project is selected and a point is highlighted in the mesh.
Note that you can use the Auto-assign by ID/Name
tool to automatically assign the imported points to existing points in the
model. When you select an active import, click the Auto-assign button 
. A
prompt will display asking whether to assign by User Name or Point ID, which
will depend on the associations between the points in the project and the
import.