Set the bed to 100, turn on the aux fan and home the machine (so the bed comes to the top). Let this sit for 15ish minutes. The P series doesn’t have a chamber temp sensor but a simple work around is to check the what the nozzle temp is in Bambu Studio. When the nozzle isn’t on it will follow pretty closely to what the chamber temp is at. You can also add a stand alone temp display that is viewable via the onboard camera.
The warmer chamber temp will well help stop any warping. Also make sure you don’t have the chamber or aux fan on during printing. Make sure the top is on and the door remains closed.