Here is an approach that is more universally applicable. Set a script connected to a button on the portal row to:
- Capture the unique identifier from that portal row (or the data they have in common) as a $Variable.
- Go to the portal table's layout
- Enter Find mode
- Set the unique identifier field to be that $Variable value
- Perform find
That works if it is a unique Secondary Key Field, or if the group of portal records have a common attribute.