Each License you get from our store is good for connecting to one QuickBooks Online Account. You can move a license around from account to account. But it will only ever be active with a single Account.
You add or move your license to your connection on your Dashboard. Log in with your Intuit account information. You should see your connection or connections. To the right of the "license" label you should be able to see an "edit" button. Click that, and paste in your license.
In the image below, you can see there are two connections. One of which is "licensed". And one is still in the "trial" stage. Notice the "edit" button. Thats how you enter you license.
Moving a License to Another Connection
If you want to move your license to another connection, just remove it from the current connection first, then add it to the new one.