Turn the Instant Pot to saute mode and cook onions until they are translucent (about 5 minutes).
Add celery, chicken stock, water, meatballs, kale, garlic, lemon juice, sugar, and basil.
Lock the lid (with vent closed) and set to manual for 4 minutes.
When the Instant Pot beeps, perform a quick pressure release (open the vent until the steam is released).
Add tortellini noodles, lock the lid (with vent closed) and set to manual for 1 minute.
Perform a quick pressure release.