In a small pan, heat the coconut oil, add the mustard seeds. Let them splutter, once done, add the pearl onion slices and fry till crispy along the edges. Add the curry leaves. And now pour this over the dal in the Instant Pot and mix well.
If you don't want to use the stove top at all and want to do everything in the Instant Pot, do this step in the Instant Pot before adding the dal and water, right at the beginning.