Could not boot into MacOS partition

Hi There,

I have Microsoft OS along with the default macOS. I was notified of the newly released upgraded version of Sierra and was asked to install it. I click to begin installation. My macbook was restarted and as the installation begins, an error pops up which halted the installation process. I was asked to press "D" for diagnose at restart.

I pressed the "D" key as my macbook restarted. I followed the instructions to test the hardware which went well. After the hardware check, my macbook restarted, but could not continue the installation.

I restarted one more time while pressing the "Options key", but this time, I can only see the windows partition (bootcamp). I do not know how to proceed to recover my macOS as I really need it.

Can you please help?

Thank you