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. [1]

In this menu, you have to click on Device Transfer/Back Up. [2]

Next, please click on Create Transfer Code. [3]

Now you have reached the end point of the menu. Just click on OK, and a new transfer code will be generated. [4]

You can copy the code, and paste it to a safe place for a future account transfer. [5] However, please don't create a new one, because creating a new transfer code will render the previously created one useless.