I now see that you are going from Basel to Zurich. Between those cities the TGV operates as a normal train. So you got a normal, domestic Swiss ticket that is valid on all trains from Basel to Zurich, and no seat reservations. And you do not need reservations. Between Basel and Zurich normal Swiss rules apply.
Note also that buying a ticket for a trivial domestic trip in Switzerland several months in advance is not necessary. This is mass transit. That train is used by commuters every day, most of whom travel on a pass, and decide which train they take at the last moment.