Much like this year’s Tom Brady situation if he were to go to the Super Bowl. It’s his first season with the Bucs, who had a losing record last year. What, if any, past quarterbacks have taken their new team that had a previous losing record to the super bowl in that first season with the new team?
Jake Delhomme might be the most recent clearly similar example, though obviously with a very, very different path through his career to that point (only a brief stint in the NFL, then more success in NFL Europe). He was signed by the 7-9 Panthers in the 2002-2003 offseason, and went on to lose Superbowl XXXVIII narrowly to Tom Brady's Patriots.
Trent Dilfer nearly qualifies; he won Superbowl XXXV with the Ravens, in his only season on the team. They went 8-8 in 1999, however, and certainly no-one would suggest Dilfer was particularly responsible for that team's success.
Another quarterback who might qualify, depending on how you count things, is Nick Foles for the 2017 Philadelphia Eagles, whose MVP-winning performance in Supserbowl LII came the year after the Eagles were atrocious, but of course he wasn't the primary quarterback for the team until late in the game the Eagles clinched the division after Wentz sprained his ACL.