It isn't possible to specifically enter P Scales in regards to steps assessment. However you could create a custom assessment markbook to record P Scales if required. For further guidance on creating a custom assessment markbook please click here.
Alternatively as a school you can decide on a mapping for the P Scales e.g. you may decide that a P8 would be similar to a 1:3 so wherever you wished to enter a P8 for a student you would use the mapped step to record it. You may find the following guidance of use for assistance with mapping the P scales: