Semenov follow the directions in the link. On the Flathub website you can find your apps, I find that's easier than using the command line for searching flatpak. One you find it, you'll see an installation command towards the bottom of the page, the install icon doesn't work. Run this command in the terminal, enter Y and follow the prompts for install. Once install is finished, you should be able to find the application in you application menu or using krunner (left alt+spacebar is the default way to launch krunner search on Solu KDE).
Edit: you can simply copy and paste the commands, to paste in the terminal (Konsole) you use shift+Ctrl+v, not just Ctrl+v.
