Thank you for your post.
You're not too far away. You need to assign a name to the first field in the second portal (Field 8?). Change the script to:
Set Variable [ $row ; Value: Get ( ActivePortalRowNumber ) ]
Go to Object [ Object Name: "Tab 2" ]
Go to Object [ Object Name: "Field 8" ]
Go to Portal Row [ no dialog ; $row ]
Go to Field [ Field 8 ]
The "Halt Script" step is included so the tab isn't evaluated after the script runs.
Let me know if you need additional clarification.