Transferring a Fate Grand Order account
1. Get a transfer number and password from the seller and load it on your device. On the title screen, there is a "Data Transfer" button on the bottom right. Tap on it and it would bring you to a screen where you need to type in the transfer code and password. Tap on the "Start Game" button. If the info is correct, you'll get a dialog with a brief description of the account that would be transferred. Confirm it and it should start downloading new data, after which you'll enter the account.
2. Check the account and make sure that everything is there and as advertised.
3. Issue a new transfer code and write it down, in case you lose access to your device. Tap on Menu ->My Room -> Scroll all the way down -> Issue Transfer Number. Type in a password, confirm it and tap the register button. It will generate a new transfer code. Write it down along with your password.
Done, the transfer is complete. If the seller went first, now is the time for you to make the payment.
Transferring a Japanese version Fate Grand Order account
The steps for transferring a JAP account are the same as for Global, but the whole game is in Japanese which might make it tricky if this is your first time playing this version. Below I will show you where you need to click in order to load a JAP account.
For most dialogs that show up in this game, the right button is usually Yes or OK, while the left one is No or Cancel.
1. Install the Japanese version of the game. If you're not from Japan, the game would not show up in Play store and you'll instead see the global version. You can get the Jap version by downloading an apk for it, or by using third party app stores such as QooApp or ApkPure.
2. When you first launch the game, a dialog will appear, telling you about downloading data. Tap on the right button to start download. After it's complete, you'll be brought to the title screen.
3. Tap on the first button in the bottom right corner, this is the data transfer option. A dialog will show, asking you to accept terms of service. Tap the right button to accept.
4. Transfer screen will show. Type in the transfer number and password on the next screen and tap the right button when done. A dialog will show. Closing it will bring you back to the title screen and the account is now loaded. But if it remains on the transfer screen, it means that the entered info is invalid.
Done, you have loaded the account. Tap on the title screen to enter the game.
Issuing a transfer code on the Japanese version
1. Once inside the game, tap on the menu button and a row with options would appear. Tap on the last one, with the icon of a phone.
2. Scroll all the way down and tap on the second last option.
3. Type in a password, confirm it and press the only button.
4. A dialog will show with the transfer code. Write it down. Press the left button to close.
Done! You have successfully completed the process of transferring a Fate Grand Order account.