Can't find MacOS after bootcamp
I installed windows 10 on my MacBook Air 2017 and have been using it for a few days. Today I wanted to go to MacOS but couldn't. Restart in MacOS option in Bootcamp delivers a error message that, "could not locate MacOS boot volume." and if I hold option on startup, two options appear. Both is windows 10. One is the one I have installed and another prompts me to install windows 10 but no Mac option appear. How can I get back to mac OS?
MacBook Air 13″, macOS 10.12