Unfortunately, but you should have unlinked your eShop account before you purchased and tried to link your new Wii U console, as there really isn't a way for you to do so now.
But give a call to Nintendo's 1-800-255-3700 (6 am ~ 7 pm Pacific, everyday) Customer Service number, or use their webform to contact them, and perhaps they can unlink your eShop account remotely, and also perhaps be able to do the same with your Nintendo Network ID that you used on your original console.