First class reservations with eurail pass

Im planning on going from budapest to vienna using the eurail global pass. I was told it was better to book directly from the train website.

So i went to the OBB page. Here with the pass i have the ticket for free but can also make seat reservations for free on first class.

My question is do i need a first class pass to make this reservation or i can still do it with the second class pass.

Thanks.