Heat oil in the Instant Pot using the Saute button. Add onion and cook until softened, about 5 minutes. Then add the garlic and thyme and cook about 30 seconds more.
Add stock, carrots, celery, and tamari sauce, scraping up any browned bits off the bottom of the instant pot.
Add the cooked chicken and the noodles and lock the lid. Cook on manual pressure for 4 minutes.
Use a quick release and carefully open the Instant Pot.