In 1949, which pilot flew over the North Pole, becoming the first person to fly over both poles, after crossing the South Pole in 1929?

Probably Bernt Balchen, who was with Richard "Dickie" Byrd on their 1929 South Pole flight and flew on his own over the North Pole in 1949, by which time that was no big deal. (Russians had a confirmed flight in 1937 & a landing on the ice there in 1948) Byrd claimed to have flown over the North Pole in 1926, but for reasons of fuel, weather, & a fishy logbook is no longer believed.

Here is a link in support of Bugnutz answer.

https://nationalaviation.org/enshrinee/bernt-balchen/