Launch Dr.Fonee and sign out of your old license account.
On Windows, click the Login icon on the top right corner of Dr.Fone. Then click the Settings icon on the popup window and choose Sign out from the dropdown list.
On Mac, click Dr.Fone in the Menu bar at the top of the screen, and click Register. On the Register window, click the Sign-out icon next to your account name.
Then you will be able to sign in with your new license email and registration code.