Place trivet in Instant Pot insert and 1 cup water. Add frozen meatballs. Seal and cook under high pressure for 5 minutes. Quick release pressure. Remove meatballs and set aside. Discard cooking water.
Add blackberry jalapeño jelly and BBQ sauce to insert. Set to low on sauté feature. Stir until jelly is melted and sauce is smooth.
Return meatballs to Instant Pot and toss to coat thoroughly. Switch to warm and serve, or remove to serving bowl and serve.
This makes plenty of sauce, you can certainly make more meatballs, if desired.