Here is how to set GB as 99GB on English version of Speed WiFi W04
1st step: Tap the red circle below
2nd step: Tap the red circle below
3rd step: Tap the red circle below
4th step: Type 99 as below and choose ok.
5th step: check if 99GB is shown as below and go back to home screen.
Last step: Check if it is changed. Done already.