mute button on iPhone 6 sticks up, or down, doesn't work

Recently bought a phone from person at my school for $50- Fixed screen and volume buttons but can’t for the life of me figure out how to fix the mute button that sits above the volume buttons. It just kind of sticks up or down and never really clicks, and it doesn’t actually work, doesn’t mute the ringer.

Do I need to buy a new flex cable / button? I’ve already tried opening it all up and blowing compressed air at it to clean out any dirt / grime, and took it all off and put it back on.

I have a video of the ringer / mute button here :

https://www.youtube.com/watch?v=Xoaenu3a...