Can't select corridor to apply cant

Hello,

I am struggling with the problem- same in my work and revisiting the training dataset.

When trying to assign cant to corridor, it would not allow me to select corridor. Tried Default (2D) model- it says this tool can't be used in 2D model. Tried Default 3D- no matter what I try to select or highlight, it says not available for the tool. It just would not find the corridor.

Two subsequent questions: how and where do I find something to snap on for this too? This is the only one that is not listed under corridor edits....

or else... is there a ways to avoid these pesky jumping up and down on-screen cartoonish boxes and select corridor from selection dialogue box?

I referred back to the training workbook, but there are no instructions where, in which model/ view, and what to select. Just says select corridor.

??????