No sound if video is in an app

This advice was helpful for one iPad. Somehow, the sound for in-app videos got muted. If I did that, I don’t know how I did it. In the newer iPad, (it’s a refurb but new to me), when I pulled down from the top right, there was a bell. The iPad I use for internet, news apps, etc., doesn’t have a red bell in the Control Center. Since the iPads are in sync, I thought what I did with one iPad, that action would effect the other iPad. In this instance, it didn’t. So, since there isn’t a red bell in the control center, I still don’t have sound with in-app videos. Do the iPads have to have a certain version of the operating system in order for there to be a red bell in the Control Center? If so, what is that version? Is there another solution to getting sound for in-app videos?

I have two iPads. I have never looked at the Control Center on either iPad, so, the red bell is on one iPad but not the other. Because I have never looked at the Control Center, I have no idea how my in-app videos got muted. But, the advice I received about seeing if the red bell was turned off solved the issue for one iPad. However, it didn’t solve the issue for the other iPad, because there is no red bell in the Control Center. That iPad is older, the one I carry around, so if I drop it or break it, I won’t feel as bad as I would if I broke the newer iPad. I also use the older iPad to search the internet, play games, etc., and its the iPad that I want to be able to listen to in-app videos on. Since there is no red bell in the Control Center, do you know of another way to get sound for the in-app videos? What IOS version does the iPad need for the Control Center to have the red bell?