If you have created an opening in a floor, you can resize or reshape the opening by clicking and dragging its edges or corners.
To resize or reshape a floor opening:
In 2D plan view, click on the opening edge you want to move.
Right-click and select Move, or select Edit > Modify Elements > Move.
To resize the opening, hover your pointer over the center of the currently selected opening edge, then click and drag the edge to adjust the opening size.