Wise owl has ended up putting two 7's in the same row and now does not have the energy to backtrack and find where he made the error.

To play interactively, get Simon Tatham's Portable Puzzle Collection (for example F-Droid or online), open Solo, and start game by Game ID:

3x3:6c5e3a1a2d2_7g8e2k9e5g2_4d5a3a8e1c3

::: spoiler First step

I don't think any more numbers can be placed without trial-and-error or advanced reasoning techniques. It's a Brutal level one, aka Seppoku, after all
:::

Edit: Fuck that, it's fake