It's fairly common for players in the NFL to play one position in college and then transition to a different position upon joining the pros.
Most cases come from an NFL team finding a player who isn't quite up to the pro-level at their position but has potential at a different spot. Sometimes it is by the player's request; at other times they receive an ultimatum from the coaches. It can even happen late into their careers (case in point: Cordarelle Patterson with the Atlanta Falcons.
A popular scenario is having a quarterback switch to a tight end or to a wide receiver. The quarterback position is highly competitive in the NFL and players who aren't quite up to the task have to adapt to survive. Again, this tends to happen more when they are drafted, but it can happen after years of playing quarterback (case in point: Terrelle Pryor).
One of the biggest "almost" was Baltimore Ravens quarterback Lamar Jackson. We now know him as an MVP quarterback, but when he was preparing for the NFL draft, coaches, scouts and general managers tried to sway him into playing running back. While we didn't get Lamar Jackson in the backfield (thankfully), we did get a few players who found success and popularity after changing their position in the NFL.
NFL position change - Terrelle Pryor
Terrelle Pryor is one of the more recent and more popular position changes in the NFL. It was also one that few people expected to happen, especially late into his NFL career.
Pryor won two Big Ten championships at Ohio State in 2008 and 2009. The Oakland Raiders drafted him as a quarterback, even though he had served as an occasional wide receiver in college. But Pryor ended up bouncing around the league for several years and found little consistent success as an NFL quarterback.
In 2015, Terrelle Pryor made an unorthodox move to switch to wide receiver permanently. While he might not have had a better career after the change, he at least extended his career. Pryor played for the Cleveland Browns, Washington, the New York Jets and the Buffalo Bills before ending his career in 2019 after being released by the Jacksonville Jaguars.