Headphone volume left-right?

For a few days now my left headphone (Bluetooth) has been much louder than my right one. (It's not my ears). I have often read that you can change this in the system settings, but I do not find it (Huawei P Smart).

Does anyone know nh app for it?

Why do you buy such scrap when it doesn't work? I'm constantly reading something about Bluetooth headphones. They seem to be the last rubbish