Guessing English may be the barrier here - but I don't understand what you are unable to do?
If you are on floor 2 in 2D view, and have the arrow/selection tool active and press ctrl-A (Windows) or cmd-A (Mac) - all items on that story will be selected...
One of the forum moderators
AC 27 USA and earlier • macOS Ventura 13.6.9, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB