I need help with MacBook Air (2011) online recovery

Instead of holding down option+command+r, try holding down just command+r. This will enter the normal recovery mode instead of internet recovery mode. From here you can follow the same steps as normal to reinstall MacOS, but instead of doing it through the internet it will install from a recovery partition on your Mac. It may be a slightly different version of MacOS (I believe it is MacOS Lion on this specific Macbook.) However, after installing MacOS X Lion you can then upgrade via the app store or whatever other methods you wish. If you need any more help, don't hesitate to ask!

Depending on the version of macOS your system is running you may not have the recovery partition. You likely lost it when you installed Windows.

The best way is using a second Mac create a bootable OS installer USB thumb drive. Do you have access to a 32GB thumb drive and a second Mac system to create the needed bootable installer?