How to deauthorize all

Thank you. That was just what I needed. I still cannot buy songs on Apple Music. I enter the song in upper left [search]. Then select iTunes Store. There is nothing on the upper right to select.

• Search Apple Music: Enter what you’re searching for (such as a song title or lyric), click Apple Music on the right, then select a suggestion or press Return.
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I have gone into preferences to select iTunes Store.