Place chicken, tomatoes, broth, water, taco seasoning and salsa in the Instant Pot. Set to manual mode and cook for 12 minutes on high.
Do a quick release of pressure.
Remove chicken and add softened cream cheese to Instant Pot. Stir cream cheese into soup until it is melted and fully incorporated.
Shred chicken using 2 forks and return to soup. Stir well and serve. Top with avocado slice and cheese.
If using frozen chicken breasts, increase pressure cooking time to 12 minutes.I did not include the time it takes for the Instant Pot to come to pressure since there are so many variables for this. It took my soup an extra 15 minutes to come to pressure so be sure to factor that into your time.