Hello,
Thank you.
I would recommend you check out this site
https://www.aosbadvicetips.com/, it is a fantastic site I found with lot's of information and also the option to buy a very useful guide.
Also look out for websites and books on the UKCAT assessments. The UK Clinical Aptitude Test (UKCAT) is an admissions test used by a consortium of UK Universities for their medical and dental degree programmes, the test format includes the verbal, numerical and abstract reasoning tests, which are similar to those sat at the AOSB.
Please don't hesitate to get in touch if you have anymore questions.
I wish you the best of luck for your Main Board.
Best,
C_R