Take a deep breath and relax the vocal cords. Try to keep them in this position while making an exhalation with air. Try to add a bit more sound to the exhalation without starting to sing. Use a lot of support and make the sound of exhalation stronger, still with relaxed vocal cords. Gradually increase the sound, but without decidedly singing.

In the beginning grunting is easier to and if you add more air and less tone/sound. Later you can diminish the air and add more volume.

You can also try to find grunt by imitating the sound like you are really annoyed.

If any of the exercises feel uncomfortable, tickle, or scratch, it is usually because you have lost the support, which means you are forcing you voice. Stop and try again with more support. Hold back the air even more.

Comply with the three overall principles of singing in order to avoid uncontrolled constriction and damaging the voice.