Having one cabinet door higher or lower than the others looks very strange. It is either that the hinges need to be adjusted, or maybe that the doors weren’t installed correctly in the first place.
If you are lucky, you will have the adjustable European hinges. These hinges are not seen until you open the door, and they can be adjusted for and up and down, side-to-side, or front-to-back movement. It is easy and fast, and all you will need is a screwdriver.
European hinges will have two screws on each hinge that you will need to slightly loosen to adjust the door for height. These screws on the cabinet wall and are at the front of the hinge closest to the opening, at the top and bottom of each hinge.
Loosen the screws at the bottom hinge first and support the door as you slightly loosen the top hinges screws. You will feel the weight of the door in your hand when you have loosened the screws enough. Move the door up or down to your liking and tighten the screws to hold the door in place. Close the door to check its alignment with the other doors. If you are satisfied, open the door back up and tighten the screws until snug.