Remove the drawer from the desk by pulling it out and slightly lifting up as you guide the back end out of the drawer opening. Put the drawer on a work surface.
Examine the drawer hinges on the sides of the drawers. If the hinges on the sides of the drawer are loose hold them in the correct position on the side of the drawer, one at a time, and retighten the mounting screws with a screwdriver.
Look inside the drawer opening and check the hinges on the sides of the drawer opening. If they are loose, hold them in place, one at a time, and retighten the screws.
Align the hinges on the sides of the drawer with the hinges on the sides of the drawer opening and pivot the back end of the drawer into the drawer opening. Slide the drawer back into place inside the desk. Open and close the drawer to make sure that the drawer is aligned properly and gliding on the hinges.