Cut ham to fit in Instant Pot if necessary. Place in Instant Pot.
Pour 2 cups pineapple juice into Instant Pot, put the lid on, turn the valve to sealing and select Manual or Pressure Cook, high pressure, for 15 minutes.
It will take about 10-15 minutes to build pressure and begin counting down. Once the cook time is over, turn the Instant Pot off and let the pressure release naturally (this can take about 15 minutes).
While your ham is cooking, combine 1 cup pineapple juice, sugar, vinegar, salt and red peppers in a small saucepan with a whisk. Bring to a boil over medium-high heat, then reduce to medium heat and simmer for 10-15 minutes until reduced by half.
If desired, combine 1 teaspoon water and 1 teaspoon corn starch and stir into simmering glaze to thicken slightly.