how do you link xbox account to steam? ( i know this is the wrong topic for it but idk where else to ask it )

Hi, ive bought this game 2 weeks ago ( had no patience to wait till it came to steam ) but now that its on steam. ( rip another 40euro's ) how exactly do you connect the accounts? i cant be bothered to start all over again tbh. love the game though. the main reason im buying it on steam is for the achievements xD would have been nice if previous owners could get some sort of coupon / discount code or something.