How to transfer iTune downloads to files on iPhone 12

i recently bought a new iphone 12, upgraded from an iphone 8, and i’m trying to make a song into a ringtone. garageband says the song i have downloaded is protected and won’t let me select it. i’m trying to transfer the song to files, but there are no prompts on files for downloaded songs, nor can i go right to the downloaded songs to transfer to files. i’ve tried mp3 converters and file converters and they haven’t worked at making the song i want a file. how do i transfer this song(downloaded and purchased through itunes) to a file?

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