Good morning suntraveler,
you can find how many miles you need by calculation:
https://www.aeroflot.ru/ikm/mobile/s...864.1527603493
I hope this link also works for you.

Check if seats are available in O class by doing a dummy booking "pay with miles" on the Aeroflot website.

Redemption by Aeroflot Bonus miles sometimes works online. If not, can Aeroflot main number (shown at the bottom of the website), then follow the menu. Their spoken English is excellent.

Enjoy!