Place the chicken breasts in the Instant Pot insert in a single layer.
Pour the chunky salsa and dark balsamic vinegar over the chicken, then sprinkle the chili powder and ground cumin evenly on top.
Close the lid and set the vent to sealed.
Press the Poultry button, use Adjust to set pressure to High, and set the timer for 25 minutes; the cooker will preheat and then cook.
When cooking finishes, let the pressure sit for 5 minutes, then carefully quick-release remaining pressure and open the lid.
Remove the chicken to a cutting board or bowl and shred with two forks.
Return the shredded chicken to the Instant Pot and stir to coat with the sauce.
Spoon the chicken into corn or whole wheat flour tortillas and top as desired.