Cut kernels from corn and set aside for now. Scrape corn again to get any remaining kernels & juices. Puree with 1 cup water and set aside.
Turn Instant Pot to saute mode and heat oil. Add poblano, onion, jalapeno, celery. Mix well. Cook, covered with a glass lid, 4-5 minutes until onions turn translucent.
Add potatoes, tomatoes, salt, allspice, corn kernels, pureed corn, and the remaining 1 cup water. Mixe well.
Close Instant Pot with the pressure valve to sealing. Pressure cook 5 minutes. Natural release the pressure.
Mix corn starch with 2 Tbsp water. Turn Instant Pot to saute mode and bring soup to a gentle boil. Stir corn starch nixture into the soup.