Flip the 3D printer on its side with the extruder assembly facing up.

Locate the loosely hanging stepper motor wire.

Gently insert the stepper motor wire into the stepper motor.

If any resistance is met you could try to flip the wire and try inserting it again as the direction of the stepper motor wire matters and little slots have been made in the plastic casing for the connector to ensure proper directional requirements are met.