iPhone 8plus

So I recently bought this phone everything was working perfectly. I’ve had it for about 5months. Today I noticed the ear speaker sounded static when listening to music or watching YouTube videos. I’ve noticed also, while on the phone it doesn’t sound as loud as it used too. Still bearable though. Literally tried everything it said to “fix” it online even reset everything, nothing worked then I did this (picture below) and boom no more static! Sounds back to normal. But I’m worried can this mess with anything else? Why does it work only when it’s all the way to the left?