Go to your board: if you need to move just one card right click and choose “move to Workspace/Iteration” from the dropdown menu as seen in the screenshot.
Then choose where you want to move it from the dropdown menus and click “move
NOTE: the card will receive a different number once it migrates to the other project.
To move multiple cards
If you want to move multiple cards at once: First hold down the shift key and select the cards you want to move, then right click any of those cards and choose “Move Cards to Workspace/Iteration.” Follow the same instructions as for a single card.