If the feat meant 'after you have attacked this turn', it would say so. Instead, it says 'when you take the Attack action'. Attack action is what leads into attacks, but these are separate things, as you can have multiple attacks per turn, the Attack Action just encompasses all of those.

Given you can use bonus actions whenever, I feel confident saying you can declare that you'll be spending your action for this turn on the Attack action, then bonus action the target to the ground, and then move into your actual attacks.