Any tool which repairs dual boot OS

Hi All,

I have installed a Windows 10 OS with a disk and I have Windows 10 along with Windows 8.1 respectively. It worked good for almost 2 months but now I cannot boot to Windows 8.1 OS.

Is there any Tool, that can repair the Windows 8.1 instead of reinstalling it since I have lots of data stored in.

Need Help.

Thanks,
Steve Delgato