Anyone know how to mark mines on it?

Click and hold. You want all the mines highlighted green and the rest ticked blue. I'd solved it once but had either missed something or encountered a glitch and had to exit and restart. When every square is cleared, marked as mine (green) or tagged with dots then you'll get a ding and the puzzle will resolve.

Marking the mines is not necessary. As long as you uncover all fields without mines, the puzzle will be considered solved by the game.