You will need to create a Custom Probe to enable the software to convert the voltage output of your pressure sensor into a pressure unit of your choice.
There are a couple of posts you may find of interest here at
To create a Custom probe within PicoScope select Tools > Custom Probes > New probe > and follow Custom Probe Wizard.
As you move through the Wizard you arrive at the Scaling Method where you can use a Look-Up Table to input the voltage output of your sensor relative to the pressure applied
Continue through the set up Wizard until complete where your new Custom Probe will appear for selection in the Library section of your probe menu under your Channel options. (Probe selection)
I hope this helps but please feedback if you need any further help