Hi! You typically want to breath out through your noise, then inhale through the mouth when you go for air.

Another tip that comes immediately to mind is try using a swimmer’s snorkel. At first, it’ll be really difficult to keep from water going into your nose but after a few practices, your nose and it’s canals will block out water as a reflex, enabling you to breath through your mouth the entire swim. Hope this helps and sorry for English!