How to link account?

I have progress on my battlenet account and I want it to carry over to a xbox pc account that ALREADY has a activision account with little to none progress, how do I transfer my progress from battlenet?

I wanna do this since bo6 is free on game pass but still wanna have my progress from battlenet on the Xbox account with game pass

(Please step by step cuz I know nothing about tech or stuff like that)