Restring

This command allows you to regain bard points you may have gained as a
bard in a previous life. To do this, simply type "restring" in the aptly
named Restringing Room west of the Bard Advancement room.
  The amount you had is taxxed for each time you've reincarnated
since leaving the Bard guild, and what level bard you are
when restringing, in the sense of tertiary, secondary,
or primary Bard.

NOTE : This will not give you your old instrument back, it will simply give
you the points. This is a good thing, because it allows you to start over
and correct any mistakes you might have made in spending the points on the
original instrument.
See also : instrument help