It's possible that you can improve motor skills slightly by using PlayStation etc shoot'em up games. It's certain that you can improve mental maths through practice, I'd argue, particularly if you've not done any Maths for five/six years (GCSE to graduating).
Here's a handy link to the training pipeline for Royal Navy / Fleet Air Arm, RAF and Army commissioned / officer pilots / WSOs and non-commissioned RAF aircrew. RN Observers stand fast.
It's a few slides in Powerpoint -
here - read, learn and inwardly digest, and be prepared to answer questions at AIB/OASC.