Put water and chicken in the Instant Pot (you can use the trivet or put chicken directly in a water). Close the lid and turn the valve to a Sealing position. Press the "Pressure Cook" or "Manual" button and set the time for 8 minutes for chicken breasts (or 13 minutes for chicken thighs).
When it's done cooking, let the pressure release naturally (NR) for 5 minutes, then quick release (QR) the remaining steam.
Take the chicken out of the pot and chop into pieces. Pour the water out of the pot, then put the inner pot back into the Instant Pot.
Press the Saute button on the Instant Pot and leave the pot uncovered.
In a cup, mix the oil, soy sauce, brown sugar and cornstarch.
Add cooked chicken and the soy sauce mixture to the Instant Pot. Cook on a Saute setting, stirring every 30 seconds, until the sauce thickens (about 4 minutes).
Notes
You can make it with frozen chicken, just pressure cook from frozen for 20 minutes for chicken breasts and 25 minutes for thighs.