Example of Untrim Surface

Select the edges as shown, set Distance to 15%, and under Options, choose Extend edges.
   
Select the edges as shown, and under Options, choose Extend edges. Select edges as shown, and under Options, choose Connect endpoints.
   
Select the edge as shown, keep the Distance at 15%. Under Options, choose Extend edges. Select the edge as shown, change the Distance to 30%. Under Options, choose Extend edges.
   
Select the face, and under Options, choose Internal edges. Select the face, and under Options, choose External edges. Set Distance to 15%. You can also select All edges to untrim both internal and external edges.
   
Select the three edges shown on the parent surface. Under Options, select Exclude parent surface and hide the parent surface.