Adjust the volume

Revit
1

How do I adjust the two ends of the volume? Here is my .rvt and .dyn1-1

1-2
1-2.jpg1081×719 53.8 KB
Slope_Analysis _Model_Select-thesis.dyn (103.7 KB)
https://drive.google.com/open?id=1jyeewVmaOp-j6qvj-e7sH-YsdN6ysMLn(.rvt)