Add the butter to the Instant Pot, once melted add the chicken.
Season chicken with salt and pepper and saute chicken until it has lightly browned on all sides.
Once the chicken is lightly browned, pour in the pasta. Stir and lightly scrape the bottom of the pot to remove any browned chicken bits. If using a nonstick pot, use a silicone spatula.
Add the chicken broth on top. DO NOT STIR PASTA! Simply just push all of the pasta down, so most of it is covered by the liquid.
Close pressure cooking lid, and move valve to the seal position. Pressure cook on high for 3 minutes.*If you are using a different shape of pasta, follow these instructions to determine the proper pressure cooking time: Take the recommended cooking time that is on the box of pasta and divide by 2 and then subtract 2. Pressure cook for that many minutes. For example, if the box recommends 10 minutes of cook time, divide 10 by 2=5. Subtract 2. 5-2=3. Pressure cook for 3 minutes.
Once the timer beeps and the Instant Pot is finished pressure cooking, move the valve to the vent position and release the pressure. If a lot of liquid starts to come out of the Instant Pot, close the vent, wait 3-5 minutes and then try to release the pressure again. Continue to do this until all pressure has been released.
Add broccoli, and stir.
Add Velveeta cheese, and stir.
Add milk and stir until the Velveeta has fully melted.