You can change the artboard order by clicking and dragging them in the Artboards panel. Then you can rearrange them into the correct order.

In the example below I have added an artboard shown as "1a" at the bottom. I want to move this between 1 and 2.  Note that the names of the artboards don't matter, only the order in which they appear in the Artboards panel.

1. Click on *Window > Artboards*

2. Click and drag the bottom artboard (9) into the 2nd position

Example:

[![enter image description here][1]][1]

3. Click on *Document Setup > Edit Artboards > Rearrange All*

4. Set the required number of columns and hit OK, and the artboards will be rearranged into the correct order.

Example:

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/4eI2X.gif
  [2]: https://i.sstatic.net/FADJ3.gif