TurboGrid is primarily for meshing bladed components. If using point data for input to TurboGrid, three files are needed: hub.curve, shroud.curve, profile.curve. Hub.curve and shroud.curve contain the (x,y,z) coordinates defining the hub and shroud curves, respectively. Profile.curve contains (x,y,z) points defining the blade surface at different span sections. The resulting mesh can have an inlet block and an outlet block. The inlet and outlet blocks have four surfaces bounding them: hub, shroud, periodic1 and periodic2. The inlet and outlet mesh blocks resemble a channel but it's not possible to control the shape of the periodic surfaces - this is controlled by the mesh topology in TurboGrid.
If the channel you wish to mesh has a specific cross-section you wish to maintain, you could import the channel geometry into Ansys Meshing and mesh it with that tool.