If you need to convert sound from one format into another then soundKonverter is the way to do it. You can add an entire directory of files and have them convert or just a single file or URL. It is a very easy program to use and gives good results.
To install soundKonverter in KDE neon open up Konsole and type,
sudo apt install soundkonverter
After installation you can find the program by going to the Applications Menu and looking under Applications/Multimedia or by selecting the Applications Menu and typing its name.
Most of the default settings are fine although you may want to have a look around and fine tune the quality and decide whether you want to apply replay gain or not.