You can try in Terminal from the Recovery Partition, it will be a (quite) complicated thing, however.
My suggestion would be:
1. Get (High) Sierra from, like wherever. You know what I mean.
2.
https://saintlad.com/install-macos-sierra-in-virtualbox-on-windows-10/
3. Get El Capitan installer from, like wherever. The older, the better (I believe installers that are available now for download have the fatal update already baked in).
4. Use your virtual sierra to build a pikified El Cap installer on an USB flash drive (they never worked for me BTW, I used a small SSD on an USB adapter), use procedures approved by MacRumours Forums
5. Fire up the Pro from this USB flash disk, reinstall and choose your future updates wisely.