Set your Instant Pot to saute. 

Pour in olive oil, and seer your pork tenderloin lightly on each side. 

Pour root beer over the pork.  Turn the saute off.  Secure the lid on your Instant Pot and cook on high pressure for 90 minutes. 

Let the pork naturally release.  Using a fork, pull the pork apart.  It should come apart without much effort.  Once the pork has been pulled apart, place the pork back into the pot with the cooking liquid.  

Place your Instant Pot on saute.  Add barbecue sauce, and additional spices.  Simmer for about 15 minutes