Pour water in the Instant Pot. Put the trivet in the Instant Pot, then place the salmon fillets on the trivet skin side down. Put the lemon slices on top of the salmon.
Close the lid and turn the valve to a Sealing position. Press the "Pressure Cook" or "Manual" button and set the time to 3 minutes on High pressure.
When the Instant Pot finishes cooking, quick release (QR) the steam.
Remove the trivet with salmon from the Instant Pot, put salmon on the plate and serve.
Notes
You can also put a piece of butter on top of each salmon fillet in the Instant Pot (under the lemon slices) to make a lemon-butter salmon. To cook salmon from frozen, increase the cooking time to 5 minutes. You can cook more than 2 fillets at a time, the quantity of water and cooking time remains the same.