Mithril Horde - Sudoku interface

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I beginning The Mithril Horde.

I entered a Sudoku room (it said "intermediate", but that's probably irrelevant).

There was a 9x9 Sudoku puzzle on the wall, which I solved on paper.

However, I have no idea how to "enter" my solution into the game.

There is a series of 9 corridors, each corridor corresponding to a "line" of the puzzle.

However, the interface is abysmal.

[Perhaps the worst I've ever seen, and I'm a retired software engineer. ]

Can someone who has figured that out please direct me?

Thanks