Into the inner pot of the Instant Pot, pour cold water, place trivet and whole butternut squash on top. Close the lid, set pressure valve to Sealing position and press Pressure Cook button on High or Manual button for 25 minutes.
Let pressure come down naturally for 10 minutes and then quick release remaining pressure by turning valve to Venting position. The squash will be hot, so remove by holding onto the trivet handles or use oven mitts, and let cool on cutting board until safe to handle.