Select a point on the surface for the split. The split will be along the lines of the surface in the u direction. One Reset will align along the lines of the surface in the v direction. You can accept the point or drag the cursor to create a gap or eliminate one side of the surface.
This surface was created with two surfaces that have been combined.
The split line was selected along the lines in the u direction and dragged to create a gap.
During the command a Reset changed the direction of the split along the lines in the v direction and dragged to create the gap.