No Sound in Windows 10 via Bootcamp
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