There is an extended explanation in the online help
→ Edit pictures with the Customize tab – PhotoLab
.
and that’s pretty much how it starts …
… …
.
From what I’ve tried, the RGB values and the L values are treated independently,
be it through the various presets and/or through manual adjustments.
To store them / save them as Custom presets …
about the Reset functionality as well as the Undo (Ctrl+Z in Windows) → also see here …