The correct resting position of the tongue – that is, when we aren't speaking or swallowing – is with its tip pressed against the palate just behind the upper front teeth, and the back of the tongue slightly lowered. As a rule, the tip of the tongue should sit where you make the sound ‘d’. In some people, however, the tongue rests in the wrong position – most often it stays down by the lower teeth, without touching the palate at rest. In this case, the tongue encourages the lower jaw to widen while the upper jaw stays narrow, which is often seen in patients with an underbite (reverse bite) or crossbite.
There is also the so-called ‘tongue thrust’, where the tongue presses on the teeth from the inside outwards. Instead of resting, it actively pushes the front teeth forward, causing them to tip incorrectly. Any deviation from the correct tongue position can affect the development of the jaws and the alignment of the teeth, which is why it is important to correct it.
This answer is for general information. Your own case needs an examination by an orthodontist.