Add chicken pieces, water and Buffalo sauce to the pot and stir to coat.
Secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- keys and program the Instant Pot for 15 minutes.
When the time is up, quick-release the remaining pressure.
Carefully remove the chicken from the pot and shred thoroughly (a hand mixer works great for this job).
Return chicken to pot along with softened cream cheese, ranch dressing, shredded cheese, and green onions. Stir until well blended, returning to SAUTE mode as needed.
Divide chicken mixture between tortillas, spreading in a thin, even layer and leaving a 1/2 inch gap around the edge.
Divide spinach in a thin layer over the chicken mixture, then roll each tortilla tightly.
Wrap each roll tightly in plastic wrap and refrigerate for at least 2 hours.
When ready to serve, unwrap and cut into 1 inch wide slices.