how do you move a piece of design on the ground floor, in a new floor

[Giovannino60]

I made a plan and put it as a ground floor in the navigator. this floor I "sprofounded" part under the quota 0, about 60 cm, this part I want to see it in a basement floor that I did in the navigator, how do I select this part of floor and put it in the basement that I just did in the navigator?

 

[DarthVader]

you have to change plan settings

 

[Giovannino60]

how do you set the 0,00 quota at the point indicated in red in the image?