When loading a specific record in your Netsuite instance, you may not see the Box Files tab in the record view:
The "Box Files" tab depends on the "Box Files Tab" script. If the script is not deployed, the tab will not appear within the Netsuite record view.
As a Netsuite administrator, navigate to Customization > Scripting > Scripts, and find "Box Files Tab" in the list of scripts. Select "Edit" and navigate to the "Deployments" tab:
Check the checkbox under "Deployed", click OK, and save your changes. Refresh the Netsuite record view and confirm you see the "Box Files" tab: