Create a Link to the Item Record in Customer Record > Sales Tab > Items subtab

1.    Navigate to Lists > Relationships  > Customers

2.    View Edit any customer record

3.    Click the Sales Tab > Items subtab

4.    Click the Customize View button

5.    In the Results tab select  Formula (Text) from the drop down

6.    In the Formula column enter the following:

CONCAT(CONCAT(CONCAT(CONCAT('<a href=https://system.netsuite.com/app/common/item/item.nl?id=',{item.internalid}),'>'),{item.name}),'</a>')

7.    Click Save.