Sometimes, you can update the firmware directly from the firmware interface (usually with UEFI firmware).
Sometimes the vendor provides a bootable disk or something that works under DOS (usual on older legacy bios firmware). In this case *only*, you can use FreeDos.
Sometimes the vendor provides only a WindowsX executable to update the firmware, where X is a specific number. In that case you need to use this exact version of Windows. That seems to be the case for the Idealpad 120s (but I have not thoroughly searched).
If point 3 is the only way to update the firmware for your laptop, the only way is to install WindowsX for the correct X. You can download a Windows 10 disk image from Microsoft, install it and use it to update the firmware. It will complain that it is not activated, but you can use it just once to update the firmware (Microsoft technically allows you to do that, so I assume it is admitted; I do not know if this respect the letters of the EULA).
But do you really need to update the firmware? If you can boot it correctly, chances are great that updating the firmware won't make any difference.
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