To Construct a Blend Between Two Surfaces

Select the Blend Surfaces tool ( Modeling > Surfaces > Modify Surfaces ).
Select the edge of a surface to start the blend.
Select the edge of a surface to end the blend.
Enter a data point to preview the result.
Note: The directions of the handles can be changed as needed. If Tangency or Curvature was selected the blend Factors can be adjusted as needed.
Enter a data point to accept the blend or reset to reject the blend.

Left: Blend with Start and End Factor set to 20%, Right: Start and End factor set to 75%