Trending @Cognizant; How to change dept from DE to ADM

Hey folks

please help me to change my BU from DE to ADM Im a React js developer 5+yoe however I have worked on support roles only and im not getting calls in DE, but earlier i used to get multiple calls in ADM

Hr is saying we cant change before 28 days but i have heard we can change it.

also please anybody please let me know is hacker rank test is mandatory to clear or attend in bench ??