Tuning the Mandolin to Itself. 1) Adjust the 1st or E strings so they are in tune to each other. 2) Put your left index finger on the 2nd or A string of the mandolin at the 7th fret and make that string sound the same as the 1st string played “open” or unfretted. 3) Put your left index finger on the 3rd or D string at the seventh fret, and tune that string so it sounds the same as the 2nd or A string played open.