Try walking or other moderate physical activity while concentrating on mouth breathing. Form follows function, which means that as you increase your oxygen demand through your nose, your body will gradually change to accommodate it by expanding your airways. Just be sure to go slow enough that you CAN breathe through your nose while doing it. Upright posture and shoulders down will also help to maximize your airway.

I saw your thread about burping. You must be swallowing air somehow! My best guess is that, as a former mouth breather, you might be making an unconscious 'gasp' through your mouth now and then and smothering it down. Maybe try some light exercise in front of a mirror or have a friend watch you to see? Overall, go slow, observe your unconscious habits carefully, and adjust a little at a time.

Thank you for reply 

1. So how do i stop "gusp" air through my mouth?

I would start by simply getting very curious and observant about what you are unconsciously doing, before trying to change anything. Just notice how you breathe, swallow, sit, and so on. Whatever you're doing to cause the burping might not be what I think it is, but if you just sit and breathe quietly for a while and notice that goes on with your body,  you might be able to become aware of it.

I think there's strong agreement on this forum that there is no magic instant fix, and you'll spend a lot of time noticing your body, and making tiny adjustments. You will need to become the expert on your own body. It's tedious but exciting. Do a couple of 'sit, breathe and notice' sessions and see what you come up with!