The rules for the "Press" trait read as follows (emphasis mine):
Actions with this trait allow you to follow up earlier attacks. An action with the press trait can be used only if you are currently affected by a multiple attack penalty. You can’t use a press action when it’s not your turn, even if you use the Ready activity.
The first sentence implies that this trait represents special attacks which involve repeated blows, but it doesn't clarify if it has to be against the first target you attack on your turn.
For example, imagine that I'm a fighter with the Combat Grab feat: if I'm facing two goblins, and I attack goblin #1 (which would give me a multiple attack penalty), can I use Combat Grab against goblin #2 even though I haven't yet attacked them?