In Java 1.12, the accessibility settings menu wasn't added yet. Instead, you can find the narrator option in 'Chat Settings', or, you can press Ctrl + B when in game to change the narrator mode.
Go to Settings > General > Auto-lock and to stop playing music, simply swipe up and pause the music. Or, go to the music app and stop the music from...
The narrator on Java Edition can't be locked. It may be that you're in a version of Minecraft below 1.12, which is when the narrator was added. Keep trying to...