They may be covered by plug covers if your screws are covered by plug covers use a putty knife to remove them.
Sliding glass closet doors adjust height.
Most sliding glass doors contain two sets of rollers one on each side of the bottom of the door.
Pick up one door panel with the outside facing you tilt the top back and slip it into the top track.
You can alter the height of these rollers by accessing the adjustment screws which are set into slots on the door s outer edges perpendicular with the rollers themselves.
Make sure to adjust the wheel assemblies on the doors verifying that 1 inch of the roller is showing.
Open your door approximately six inches and watch the gap between the door and frame turn the adjustment screws with your screwdriver until a uniform gap is achieved.
Locate the adjustment screws on the lower edges of the door.
Repeat this step for the front door.
Usually it is simply a matter of inserting a screwdriver into the hole at the bottom of the door locating the adjusting screw and tightening or loosening it depending on whether or not you want to raise the door or lower the door.