Preheat oven to 375 degrees. Prepare a 9x13 baking dish with non-stick cooking spray.
Combine the chicken, onion, carrots, celery, peas, garlic, thyme, pepper, salt, and chicken broth inside instant pot.
Close the lid and set the pressure release valve to sealing.
Press the manual or pressure cook button and set to 12 minutes.
Natural pressure release for 10 minutes and quick release remaining pressure.
Carefully remove the chicken and transfer to a cutting board. Cut the chicken into bite size pieces. Add chicken back to instant pot.
Press the saute button on the instant pot and bring the filling to a boil.
Whisk in the flour until completely incorporated and cook until the sauce begins to thicken, about 3 minutes.
Stir milk and chopped chicken. Stir gently to combine.
Allow to boil, stirring often to avoid scorching, for about 5 minutes or until the sauce has thickened and coats the back of a spoon.
Transfer the chicken filling to the prepared baking dish.
In a large bowl, whisk together the flour, baking powder, and salt.
Add in the cold butter and mix together with a fork until the flour forms little pea sized crumbles.
Slowly mix in the milk until a dough forms.
Knead 8-10 times and turn out onto a floured surface.
Roll the biscuit dough 1/4 inch thick and use the top of a glass (or cookie cutter) to cut out 2 inch rounds of dough.
Once you run out of cutting space, squish the biscuit dough back into a ball and roll out and cut again.
Place cut biscuit dough evenly across the top of the casserole.
Bake uncovered for 30 to 35 minutes or until the biscuits have browned slightly and cooked through.
Allow the pot pie to rest for 10 minutes before serving.