The NightJet 402 and the InterCity 60402 are two different trains but run together for the Basel SBB connection to Amsterdam Centraal. The trains are attached but not internally connected (i.e. it is not possible to move from one train to the other).
If you want to reserve a seat on the NightJet 402, you can usually do that here. If you encounter difficulties, you can contact us by phone at 0848 44 66 88 (CHF 0.08/min.) or book your seat at any SBB counter.
Please note that on the InterCity 60402 (with only seats, no sleeping cars or couchettes), seat reservations are not compulsory and you can travel just with your Eurail Pass.