Press and hold your mouse to aim and fire for desktop versions. If your gun is facing the direction of your mouse, the gunnery mechanism should work also.
I also tried 0.5 seconds, 1 second, and 1.5 seconds, but there was no response.
Also, if I don't press any keys on the keyboard from the first time I start the game, the player automatically looks down. Could this be because the downloaded game is broken...?
I've checked the download link right now, and it's not broken. If your device is a tablet/console and is not using a mouse as an input, you might need to download the mobile version of the game.
