My baby is 4 months old and I'm starting to introduce bottle to him with my pumped breastmilk but he is refusing and cries endlessly. How can I make him take the bottle?

Gonna do it gradually as the baby may not be able to adapt to the sudden change. Change a few different of types of teats for him till he is most comfortable with. Try bottle feed him by others as he most likely still prefer latch when with u. May also try to play some soothing music when feeding him.