Server Error 500- Can't access admin!

I am fairly new to wordpress. I wanted to Add Menu Descriptions & Featured Images to WordPress Menu Items. So I went to the website below and copied some code into the end of my function.php file. after doing this now I can’t even access the dashboard nor logi in to my admin. I looked into my host (bluehost) to see if I could find the function.php file under the wp-content–>themes but the file is not even there. Please help.

https://wpsmith.net/2011/how-to-add-menu-descriptions-featured-images-to-wordpress-menu-items/

I am using FoodBlog Pro theme