Adding a new board to For King & Parliament

I’m VERY new to game editing and right now am completely stumped.

I want to add a new game board choice to the game For King & Parliament. The game at present has four board options, with different dimensions. But there is NO 12 squares wide by 10 squares deep board available.

Can someone please tell me the steps to create a 12 squares by 10 squares grid and import it to the subdirectory and align it with the grid.