Est-ce que tu utilises la Duolingo app? If you're on a tablet/smartphone, you can go to your device's settings, and then add the Russian keyboard. Otherwise, once you're already typing, you can just long press the 'comma', and then you'll get a little dialogue box saying 'Input settings', with two options (Languages and Android Keyboars Settings). Tap on 'Languages' and voilá! You'll get the list of input languages, select Russian and you're good to go.
Hope this helps :)
If you're on windows (and presumably other brands), you can go to settings. Once there, you go to:
Time and language>region and language>add a language>select Russian
Once you want to switch to Russian keyboard, look at the bottom right-hand side where it says ENG, and click on it. Then click Russian keyboard, and boom.