Hello Kuro! Good luck with Your Test.
Let me give You some advice, how to make Your brain training. You don't need to spend much time on it. Research show, that short, but intense sessions are better. You need only 20 min session every second day, but make that short session very intensive. The best game we have for You is Dual N-Back, and I recommend You to stick with it. You may use the classic DNB or Single N Back or both - whatever You like. DNB training improve attention and visual spatial ability, very important on taxi driving.
If You need to remember names of street, try mnemonics, especially memory palace. This guy just remember with that mnemonic all London map, with every street and object on it:
If You need more advice, please ask :)