Make marks through the pre drilled attachment holes onto the door proper.
Gap under new front door.
Pilot hole the marks.
A visible door gap between the door and door frame.
Remove the frame screws from the hinge you identified but leave the.
Place the sweep at the bottom of the door and align the sweep edge so that it blocks the door gap.
Water leaking around the door or water leaking under the door or door bottom.
Open the door and place a wooden block or hardback book under the outer corner of the door to hold it in place while you work.
Water leaking from the top of the door frame.
A door gap resulting in light under the door or peeking around the edges of the door.
If you have a large gap at the bottom of your door that may be helping the door to stay plumb.