You can do it one element type at a time - i.e. select all walls then all slabs, etc.
Then just click on the 'Home storey' in the info box and choose 'Select Storey" and chose the storey you want the elements t be on.
They should retain their relative height in in 3D and appear unmoved.
This was in 16 - it is different in 17 though.
You must use the 'Relink Home Storey' command (Edit menu > Element Settings > Relink Home Storey).
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11