Quick Answer: There is no back button in Liquid Notes that allows you to revert to a previous chord setting.
Reverting to a previous setting for a chordWhen opening in project Liquid Notes, the software performs a track type analysis and harmonic analysis of your MIDI arrangement. This enables it to get a deep understanding of your song, from detection of tracks and chords to correlations between notes over your entire arrangement. Liquid Notes uses this 'knowledge' for reharmonization, i.e. enabling you to make changes to the harmonic progression of your song.
When making a change to a setting of a chord in Liquid Notes, the new setting of this chord causes a recalculation of the entire song to reflect on the changed harmonic 'landscape' of your song. I.e. the new chord's setting means that your song, from a harmonic point of view, has changed and follows a different harmonic progression now.
With Liquid Notes always looking at the harmonic progression of your entire arrangement, more often than not, resetting a chord will not produce the original constellation of all single notes in the respective chord region. However, a reset will produce the same harmonic constellation as in the beginning. The reason for that are changes in the harmonic landscape of the song. If predecessor and/or successor chords have been changed, then it is very unlikely that the original notes of a chord that is reset will fit the new chord path. Liquid Notes ensures the "path of least resistance" for all notes.
That also explains why a history function (Step Back/Forward) would be of not much use in Liquid Notes. Changes of a chord affect its harmonic environment back and forward in time. Every change of a chord has nonlinear consequences which could only be undone in a linear fashion if you stepped back along the exact path of changes. That, however, contradicts a creative process.