Hey, I had this problem myself. The way I solved this was by first removing the earpiece (see ifixit for how to). Then remove the gauze by removing the inside of the earpiece. There was a lot of dirt here so the sound didn't come through enough. You can remove the gauze by first removing the cable from the camera and sensors. Then using the metal tab to push up (see picture) Then you have to clean the gauze with an old toothbrush. It is best that you also clean the gauze that is still attached to the screen. Then you have to assemble everything again as you would assemble the speaker. Don't forget to put the gauze back in first. Good luck, I hope it helps For me it worked perfectly, sounds like new!

To be honest, i didn’t find it that hard. First remove camera from inside. Then heat up the glass en try to poke it with a flat screwdriver. Then try getting all the glass parts out. You can reheat it sometimes (makes it easier). When all the glass is removed, use a cotton bud with some nail polish remover to remove all the glue from before. After that you just need to put in a new glass, and afterwards the camera and the screen again…and done You should take your time, and be a careful but it’s okay to do! I hope I could help

For people from Europe, I bought the battery on the following link…works fine

https://www.akku-wechsel.de/shop/tt2040