How do one stop mouth breathing?

Everyday I wake up with saliva on my pillow and I been breathing with my mouth for 19 years, no one has ever noticed it until I realized myself after stumbling upon this thing. My jaw is also cooked bcs of this but better late than never.

The reason is prolly bcs i often have my nostrils blocked so I develop this habit of breathing with my mouth instead of nose.

What effective ways I can try, I'm trying the mewing technique so i can breathe with my nostrils but it's hard for me during sleep so should I tape my mouth while sleeping or what should i do to overcome this?