What should I do if my baby doesn't sleep in the night?

A few things you can check:
1, does your baby sleep a lot during the daytime? If so, you need to tell him/her when is daytime and when is night. Train him/her to sleep more during the night
2, Is your baby hungry? Baby will wake up if they are hungry. Make sure they have sufficient food before going to bed.
3, how is your baby's sleeping environment? Make sure the room temperature and humidity are good for sleep. Also, try to have a silent and dark environment for the baby to sleep.