Play the 5th fret harmonic on the 4th string, then play the 7th fret harmonic on the 3rd string. The trick is to make sure that both of the notes are ringing at the same time. So you may want to use your right hand thumb rather than you finger, so that you don't accidentally stop the 4th string when you pluck the 3rd string. Watch this video of me tuning the 3rd string.

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Next play the 5th fret harmonic on the 3rd string, then play the 7th fret harmonic on the 2nd string.

Then play the 5th fret harmonic on the 2nd string, and the 7th fret harmonic on the 1st string.