If you would like to transfer an account to another without linking it to Facebook, you have to generate a new transfer code, because transfer codes only work once.
First, you have to log into the game and click on the menu button. 
In this menu, you have to click on Device Transfer/Back Up. 
Next, please click on Create Transfer Code. 
Now you have reached the end point of the menu. Just click on OK, and a new transfer code will be generated. 
You can copy the code, and paste it to a safe place for a future account transfer.  However, please don't create a new one, because creating a new transfer code will render the previously created one useless.