Very limited information given.
But, SPC is not used to identify outliers because it use Process Data to derive the control limits.
How about using "Analyze > Screening > Explore Outliers>" tool in JMP to identify the outliers?
For univariate data, you can use Quantile Range or Robust Fit Outliers to detect outliers
But if you want to specify the "sigma = 3", maybe you want to use Robust Fit Outliers using robust method.
![WebDesignesCrow_0-1683511338492.png WebDesignesCrow_0-1683511338492.png](https://community.jmp.com/t5/image/serverpage/image-id/52628i1243F8BDD3A1EDF3/image-size/medium?v=v2&px=400)