i am looking fot a manga that has a main character that was transported to another world and he was turned into a white dragon. i know this series exist because i read it before but now i can not find the name to loock it up again

Um, main character isn't a 'he', but I'm pretty sure the light/web novel Dragon Life (Novel) fits your description if you want to try it?

This is probably not it because its a light novel and the reincarnation goes the opposite way, but you description reminds me of Sayonara Ryuusei Konnichiwa Jinsei (Novel). The main character is a white dragon that has been reincarnated into a human.

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First think you for helping me. the book iam taling about had factions with dragons being the ruleing class

Maybe Legend of the White Kingdom?

YES THINK YOU