If you have one or more Events selected (even of different types) you can move them using the mouse, just as with any object in Cubase VST (select the arrow pointer from the Toolbox). Only horizontal movement matters.
If you are only moving one tempo Event, its position is indicated by a vertical line. If the selection contains several tempo Events, a rectangle encompassing the area from the start of the first selected Event to the start of the last selected Event guides you. The movement snaps to the closest Snap value.
P A block of tempo data that you move, always replaces any existing tempo data on the position you move it to. You cannot move the first Tempo and Time Signature Events. If you hold down [Alt] and move Events, you are duplicating them. Everything else is as when moving.