The sleep facility will find the correct pressure and they program it into the cpap machine. You can change your pressure on your cpap. Search your cpap on google or YouTube and it will show you how. Many times it’s as easy as holding 2 buttons down until the new screen comes on.
Some cpaps have an auto function where the pressure settings change based on how much pressure you need at different times. So you do not need to know a specific pressure which makes it very easy to set up.