Select the triple bar that’s next to your username icon in the upper-right hand corner of your screen.
When you click on that, you’ll see all of the categories listed.
Choose Casual Discussions, and click on it.
When you click on it, you’ll see a small round circle to your right at the right side of your screen.
That circle affects the Notification settings for that particular forum.
Click on that circle, and you can make your choice of how you want your setting to be.
You can take it off of Mute, and set it back to Normal.