Place one cup of water in Instant Pot. Place trivet into Instant Pot. Cut the spaghetti squash in half and cut out the seeds in the middle. Place halves in the Instant Pot and set to Manuel for 7 min "sealed".
While squash cooks, melt the cheddar cheese and cream cheese in the heavy cream over medium heat in a small saucepan and continuously stir until all melted and combined. Season with salt and pepper
Once Instant Pot is done, manually release the pressure immediately. Be careful the steam is hot! Once the manual release releases all the pressure, remove the spaghetti squash from the Instant Pot and use a fork to pull apart the strands.
Place the spaghetti squash into an oven-safe dish and pour the melted cheese sauce over it and gently mix well until combined. Place in a 400-degree oven until the top of the spaghetti squash becomes golden brown and the cheese begins to bubble. Enjoy!