Add olive oil to the Instant Pot. Using the display panel select the SAUTE function.
When oil gets hot, brown the meat on 2 sides, 3 - 4 minutes per side. Meat will not be cooked through. Do not crowd the pot--you may have to work in batches. Transfer browned meat to a shallow dish and cover loosely with foil.
Add garlic to the pot and saute 1 - 2 minutes more.
Add broth, juices and zest to the pot and deglaze by using a wooden spoon to scrape the brown bits from the bottom of the pot. Put the meat back into to the pot, turning once to coat.
Turn the pot off by selecting CANCEL, then secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- keys and program the Instant Pot for 20 minutes.
When the time is up, let the pressure naturally release for 15 minutes, then quick-release the remaining pressure.
Carefully remove the meat from the pot to a cutting board. Allow to cool for 5 - 10 minutes and then slice thinly.
Split rolls lengthwise. Brush mustard on the bottom half and melted butter on top half.
Top evenly with pork, ham, and swiss. Set under the broiler just until the cheese is melted, 1 - 2 minutes.