Ok a forum or a thread?
If it's a thread then you should see a option to Board-Move in the Mod Options pull down in the thread itself and once you select that it will prompt you to:
Please enter the Board ID of the board you wish to move this thread to:
Please enter the forum number on that board you wish to move this thread to:
Here you would enter the board ID and then the forum number you want to move the thread to.
A forum adoption would be a way to 'move' a forum-but it would still remain on the original board-you can see a example of this in the Board showcase forum here on the Support board as the top Forum hasa [A] next to it to indicate it's a adopted forum.