Whisk together soy sauce, brown sugar, balsamic vinegar, and water. Add to the pot. Lock the lid with the steam valve closed. Set to PRESSURE COOK or MANUAL for 15 minutes.
When cook time is up, allow to natural release for 5 minutes, then turn the steam valve to the venting position. Remove lid once the float valve drops down. Transfer pork to a cutting board and set aside.
Switch pressure cooker to SOUP setting. Once boiling, stir corn starch into the 4 tablespoons cold water until dissolved, then pour into the pot and stir until thickened to a glaze.