You install the new CT alongside the old, with the same orientation, and do not check “allow negative values”. So on one you should see both positive (import) and negative (export) values. On the other you should see the same positive import values, but the export values will be changed to positive. It’s a little complicated, but the math is explained in the link.
Once you have a day or two of data, plot the two with Graph+ so I can see that it’s correct and I’ll show you the scripts you need for import and export.
If you call the input that allows negative values “NET” and the input that doesn’t allow negative values “ABS” (absolute value) then:
Import = (NET + ABS) / 2
Export = (ABS - NET) / 2