Kryten invents a new device, coined the "quantum skipper", which Rimmer uses in an attempt to find a universe where he is more successful.
While Lister shows little care over it, Rimmer is angered and insults the other three, claiming he should've surrounded himself with people more successful than him (with them pointing-out that they are).
Later in the day, Kryten notices a strange phenomenon on the monitors, which turns out to be a disruption in spacetime that reverts their timeline to one where their actions are or aren't taken.
After regrouping, the crew discover it was Kryten's new invention, the quantum skipper, which caused the error in time.
[3] Writing for Cultbox, Sophie Davies summed up her feelings on the episode, "Next year will mark 30 years since Red Dwarf first appeared on our screens, and unless Dave commissions some sort of anniversary special sharpish, 'Skipper' functions perfectly well as a celebration of the show.