If you wish to delete the Opening Section boundary:
Make sure the Opening Section View is selected.
Select Delete Opening from the Sidebar, the Opening menu or the right-click menu (right-click anywhere in the Opening Section View or directly on any segment of the Opening Section boundary).
The Opening Section boundary will immediately be deleted.
Notes:
When you delete the Opening Section boundary, any support you have defined (e.g. bolts or shotcrete) will also be deleted.
If you accidentally delete the Opening Section boundary, don't panic !! You can easily restore it with a single mouse click - just select Undo, and the boundary will be returned to the screen, along with any support which existed before the boundary was deleted.