The first thing is to check the LCD screen and see if the microSD icon is shown. The user manual:
page 4 shows what the icon looks like. The microSD is part of the testing procedure of OpenSprinkler so it should work, but it’s possible that it has come loose due to shipping. If the microSD icon is not shown, or if it’s shown but still not recording log, the best solution is to open the enclosure, locate the microSD card (close to the top edge of the circuit board, partially under the LCD), and re-plug in the card (or change to a different card if you have a spare one).