I recently installed Windows 10 using Bootcamp. When I try to turn up the audio nothing happens. I went into device manager and the High Definition Audio Controller has a triangle with an exclamation mark over it. I tried to update the drivers but it said they were already up to date.
Sounds like you're missing the Boot Camp software needed for your Mac or it didn't install the audio driver properly.
Try downloading and running Tim Sutton's excellent Brigadier while in Windows. It should download the latest compatible boot camp software for your model Mac. Once downloaded run the Boot Camp setup file from /Users/(your username)/BootCamp-****/ and reboot when asked. Should be fixed.
Brigadier is here https://github.com/timsutton/brigadier