OK I just found it...at the BOTTOM of the screen. In the actual convo, hit the three bars on the upper right. A side panel will slide out and at the bottom is the muted bell icon. Tap it and voila! (It turns orange.)
No down arrow
I have an S6 and there is no down arrow next to the name in the thread but I see a little bell with a bar through it next to my daughter's name. Getting really frustrated! Been to every setting imaginable.