ACBVASS / NMCHRM / PBJOV
each CAPITAL letter is a capitals capital letter.
1) To work out the 3 hidden countries you will need to find the country of each capital city.
2) When you have the 3 countries, give the 3 capitals of the 3 countries, the magic letter is 'B'
Answer in Comments Section below:
If not solved by 11th Sept. ............. little hint given.