This is my understanding. I will take the time to find online sources if you ask for them. The conversion of Scandinavia was very slow, taking many centuries.
It began with Anglo-Saxon missionaries making missionary attempts I think in the 700's, which only succeeded spot meal, converting occasional villages, but not whole areas or kingdoms. The adoption of the Christian God actually happened during the age of the Vikings, who learned the religion during their many raids, especially in Normandy and Ireland. However, they did not fully convert, but simply accepted the Christian deity as another god among their many gods. Later, there were kings, especially in Denmark, who tried unsuccessfully to convert people to Christianity by inviting in missionaries etc. Ultimately, it was not until the 1100's if I remember correctly, that Scandinavia really became what could be called Christian.