I have xml libraries on my PC that I want to transfer to itunes so I can play music on my iPhone 6

I have xml libraries on my PC that I want to transfer to iTunes so I can play the music on my iPhone 6. This is old music that I transferred originally from CDs. I was able to store in iTunes and play on older iPhones, but disappeared and I can't find a way to transfer it to newer phone. This same music is available on my old iPad 2, which I have not manipulated, except to play