Set Instant Pot to "saute" and heat 1 tbsp oil in the bottom of the pot. Place pork into instant pot and discard marinade from ziploc bag. Add pork and cook for 3-4 minutes on each side.
Remove pork from instant pot and add 1 cup of Cola and 1/2 c water to the Instant Pot. Use a wooden spoon to deglaze the pot (make sure all of the stuck-on bits are scraped off the bottom of the pot). Return pork to Instant Pot. 4. Make sure valve is set to "seal" and set the Instant Pot to Manual for 27 minutes. Allow it to natural release for 15 minutes. Release any remaining pressure. Remove pork and discard cooking liquid. Shred pork and set aside.
Combine 1 cup Cola, green chilies, enchilada sauce and 1 cup brown sugar in a blender and blend until smooth. Add more Cola as desired to thin.
Add shredded pork back to Instant Pot and cover with sauce from blender. Stir to coat, and cook on "keep warm" for at least 30 minutes.