First you may need to set up a dynamic group for your Pupil Premium and Non Pupil Premium students.
Head to Reporting > Data Digger, and click on Manage Dynamic Groups to see if such groups have been set up previously.
If not, on the front page of Data Digger, from the first dropdown select Pupil Premium. Then click on the number in the circle, give the group a name and click on Create Dynamic Group. Repeat this process with Not Pupil Premium.
Then use your Merits report. From the Group dropdown, scroll to Dynamic Groups and select Pupil Premium, then Choose to run the report.
You can download this report, then re-run using Not Pupil Premium as the Group.