If you have the Biab Plugin version you can just load your song.SGU into the Biab Plugin then use the "Biab Plugin Chords" button in ReaTrak or use script below, just unfold it save it then reload it (save it with a new name as to not affect the original). You need to open bb\Song.txt when prompted (first run only).
Biab Plugin Chords to Reaper

ReaTrak import chords from biab plugin.lua