itunes deleted music

Hello,

My son downloads music through a third party app called MP3 Rocket, I saw some other articles about this third-party app but none with a solution I need. He's been using MP3 rocket to download music to iTunes for years. Recently Itunes deleted all of his downloaded music. My question is, is there any way to find the past downloaded music anywhere on My Pc, and if I do find the past downloaded on my PC, how do I get it back to my iTunes account.