Hello, 

I am afraid that you cannot process the WorldView-3 SWIR bands alone as the Red and Near Infrared channels are required in ATCOR. The only way to atmospherically correct the SWIR data is to merge it with the MS bands first. You can use Tools | Data Merge in Focus to combine the WV-3 MS and SWIR bands into the same PIX file. This is similar to the Sentinel-2 workflow outlined in this tutorial: https://support.pcigeomatics.com/hc/en-us/articles/115002140723-Working-with-Sentinel-2-Data 

If you have any questions or concerns you can contact support@pcigeomatics.com

Hope this helps,

Sarah