Importing information to categories ?

Hi,

I re-assemble my tracks on Itunes, and since a year have been adding to the 'composer' category in Itunes the label of the track as there was no 'label' category. I realized now that in Rekordbox there is the 'composer' category but not in the USB itself meaning I can't search labels.

I saw that there is a label category in Rekordbox, so I could insert now manually every label for every track, but that would take ages. I have to find a way to do this at once. Been searching for a solution but can't come up with something... Appreciate the help!