As a part of Collected Company's resolution, two creatures may enter the battlefield at the same time. If both these creatures have ETB triggers, the controller gets to choose what order they go on the stack.
Harbinger of the Tides has an ETB trigger that reads:
When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.
Bounding Krasis has an ETB trigger that reads:
When Bounding Krasis enters the battlefield, you may tap or untap target creature.
If a Bounding Krasis and a Harbinger of the Tides entered the battlefield at the same time due to a spell such as Collected Company, would the controller be able to target an untapped creature with Harbinger's trigger and then tap it with the Krasis trigger on top of it on the stack?