Snap to midi in Gsnap with pre-prepared midi file

How do I use the “Snap to midi” function in Gsnap?
I use a pre-prepared midi file (exported from Musescore if that is of any interest), and would like to snap a vocal track to it.
I use Audacity 3.5.1 on an Win11 operating system.

Please assume I have no knowledge of how the plug-in or Audacity works XD

Thanks a ton in advance. I’d be especially grateful to have screenshots.