It would help if you could measure the scale length; octave mandolas (or octave mandolins, depending on where you live) vary enormously in this respect. Generally speaking the clue is in the name; an octave mandolin is intended to be tuned an octave below the mandolin, and therefore GDAE. Some people like to play more chords than melody, and often tune to GDAD, which is a common bouzouki tuning. Post the scale length, and I'm sure some of the luthier types on here will help out.
Tim