If the Attach button doesn't appear on the Gdrive tab your NetSuite Admin will need to add full permission(s) to the NetSuite role your user is using (on the Custom Record subtab) for the following records.
Step 1: Go to Permissions> Custom Record and add the following records:
Celigo GoogleDoc Association
Celigo Google Control Panel
Step 2: Go to Permissions> Lists and add Document and Files.