Move all assets?

I may be being thick, but I can’t work out a way to move all assets (including landscape, etc.,) at the same time?

Selecting more than one means that “Multiple values” is shown in the location values on the Details pane and it is greyed-out.

Selecting a folder in the outline view and selecting “all descendants” allows a delta transform (‘Lock Actor Movement’ unticked) but the selected items don’t move (is this because they are not “movable”?).

There are 961 actors in this level, so I don’t fancy changing them one at a time.

Any suggestions gratefully received!
TIA