I will teach you step by step how to dissemble the device and replace the damaged buttons.
Unscrew the screws on the top side of the device.
Take the top lid off of the device.
Unscrew the screws holding the pink button sheet.
Remove the button sheet off of the device.
Examine the button sheet to check for any damages that may prevent the buttons from working.
Examine closer at the button sheet for sticks on the opposite side of the buttons.
If the button sheet or button is damaged, you may need to purchase a new button sheet to replace the damaged one.