Wash green mangoes and wipe them with a paper towel. Peel them using a knife and cut the flesh into slices. Discard the seeds. Add the sliced mangoes to the instant pot along with water.
Close the lid of the pot and set the valve to the sealing position. Press PRESSURE COOK and set the timer to 5 minutes on high pressure.
Once the timer goes off, let the pressure release naturally for 10 minutes. Release the remaining pressure manually by moving the valve to the venting position. Open the lid of the pot and let the mixture cool down completely.
Transfer the cooked and cooled green mangoes to a blender.
Add mint leaves, granulated sugar, roasted cumin powder, and black salt to the blender and blend to make a smooth paste.
Transfer the mango mixture to a large bowl or a pitcher.
Add chilled water and stir well.
Refrigerate the aam panna drink for a few hours and serve chilled in tall serving glasses with a few ice cubes. You can keep it refrigerated for 3-4 days.