none I'm not currently on my desktop but I think I can give you clear intstructions.
First, go into the directory you installed flarum. There you will find a file called config.php. open it with your text editor. You will find a line called debug where the value is set to false. Simply replace false from true and save that file. Now when you face errors you can find debug there!
I will attach a screenshot if I'm able to get to a pc.