How can I repair the install of macOS on a 2012 era machine that has Bootcamp partition disk layout?

I have a mid-2012 Intel Macbook Air (256GB) which is physically fine. I had bought it second-hand in 2017 & the seller specified that it was only running Windows 10 & did not have macOS installed. He had updated Bootcamp Windows 7 to Windows 10. Now I want to use it for macOS but I can't access the Mac partition because it doesn't exist on that machine. I tried all the Command+R, Command+Option+R key combinations, but nothing worked. The Bootcamp assistant software is also missing. Also tried to use a USB stick to boot from but wasn't successful. :( The disk partitions currently looks like this: How can I restore macOS function while preserving my windows installation?