Use Sort to change the order of Block in the Blocks tab of the Inspector. Reordering is available only on desktop devices.

Entering Sort mode, reordering Blocks, and leaving Sort mode.
If you leave Sort mode without making changes, the order remains unchanged.
Sort mode supports every Block type shown in the Blocks panel. There is no separate undo action after leaving Sort mode, but you can activate Sort again and move the Blocks back into their previous order.