Musiclily Pro R15J 3R3L 15:1 Ratio Full Sealed Machine Heads Tuners Tuning Pegs Keys with Big Hex Button 45 Degree Screw for Acoustic Electric Guitar, Chrome

If you've tried the obvious things and it no longer works, you might just need a replacement tuner. Thankfully, this looks like a very common tuner type, and anything that resembles Grover Mini Rotomatics should work. Here, I found a full set for <$20: https://www.amazon.com/Musiclily-Sealed-Machines-Electric-Acoustic/dp/B075N9QMBB