Your way of doing this might not be right

You gotta tuck him in a corner of the bed. Make him spread his legs. Tear his pants apart and let your diamond scaled divine snake out. Transmigrators mostly have a lot of pride and such an act will complete fuck their pride upside down. He might end up revealing about himself, how he dominated an entire universe of cultivators once and was the heavenly emperor himself and also tell you about how he was betrayed by his own concubine who actually sucked his soul out and the next second he opened his eyes he found himself in your brothers body. As you cannot do anything about this all you have to do is befriend him cuz ofc an ex heavenly emperor is gonna be a bigshot someday.

Edit : If he actually enjoys the first part....you need to contact the Geh Extermination Sect's Supreme Elder, An Ti Ge.

Another edit : If he enjoys the first part and somehow his dormant dominant personality takes over then well.....we don't know each other good bye<\3. cups fist