Push the “Sauté “ button on a 6 or 8 quart Instant Pot multi-function pressure cooker until it sets to "normal" heat. After 3 minutes, the pot should be very hot. Add the oil and wait 1 minute until the oil is very hot. Add the chicken thighs (rolled up, not flat) and cook about 4 minutes on one side or until browned. Turn them over. You can brown the other side for extra flavor but one side is enough to give you some caramelization and flavor.
Add the teriyaki sauce and 2/3 cup water to the pot and to the pot and scrape any browned bits from the bottom of the pan with a wooden spoon, moving the chicken around to mix everything together. This is called deglazing the pan. There is so much flavor in this mixture!
Place the lid on the Instant Pot and turn the pressure valve to "sealing". Make sure the silicone ring is in place inside the lid before sealing.
Push the button “Pressure Cook” until it sets to "More" or "High", not "Normal" or "Low". Some models say “Manual”. Push the +/- button until the number reaches 8. (It will cook for 8 minutes.) It will take about 8 minutes to come up to pressure, then the IP (Instant Pot) will beep and start counting down from 8 minutes. After 8 minutes, it will beep again.
At this point, you can push the pressure valve to Venting for quick release, or, let it release pressure naturally-which means do nothing at this time. It will take about 12 minutes for the pressure to release naturally and the pin will drop letting you know you can open the lid. Quick release will only take a minute to release. If you have very large chicken thighs, the natural release is a good idea but I didn't notice much difference. The thighs were tender with both methods.
If you like your teriyaki sauce a little thicker, push “Saute” button again to "More". Stir together cornstarch and 1 tablespoon water in a custard cup. When the sauce mixture is bubbly, pour the cornstarch mixture into the liquid chicken mixture and immediately stir until slightly thickened-about 30 seconds.
Spoon the teriyaki chicken thighs and sauce over rice. Garnish with green onions, if desired.