Cut off the root ends of the green onions, cut them in half--separating the green halves and white halves. Chop the green ends into tiny pieces and set aside for garnish. The white halves will go into the soup when it's cooking, so just set them aside until called for.
Pour the broth, roasted nori pieces, and kombu (if using) into your pressure cooker pot. Press the SAUTE button until it says LESS. As the broth is warming up, you may need to add a little more water if the Instant Pot gives you a "hot" signal.
In a small bowl, add the miso paste and 3 T of hot tap water. Stir until smooth and creamy. Add to the pot. Stir well to combine.
Add in the white halves of the green onions. These are for flavor and can be removed when serving because you will garnish with chopped green onions.
Add in the mushrooms and tofu and stir well.
Finally, add in the chopped chard.
Cook for about 5 minutes, then cover with the lid, set to SEALING, and press CANCEL then WARM. Let the soup simmer on the warm setting for about 15 minutes (or more) until ready to serve. Serve over cooked noodles and garnish with chopped green onion.