The cover plate for the average kitchen or work room flourescent light fixture simply hangs in place until it is removed to replace a flourescent light bulb or ballast. Though it is a simple task to complete, no repairs can be made on a flourescent light fixture until it is removed because everything that makes the light fixture do its thing is located underneath the cover.
Place a step ladder or stool under (but not directly under) the flourescent light fixture.
Climb up the ladder or onto the stool so you are close enough to the fixture to find the cover hangers, located on the sides of the fixture. There may be a lip across the whole length of the fixture for the cover to sit into, or there may be two hooks at each end of the fixture for the cover to hang from. Look at the fixture and find the cover-hanging feature designed into the light fixture.
With the light cover in both hands, hold the cover up to the fixture on a 45-degree angle and hook the side of the cover farthest from you onto the light fixture.
Lift the side of the cover closest to you up to the hangers on the other side of the fixture (the side you are on). While gripping the upper edge of the light cover, bend the cover gently towards you and lift it up above the hooks.
Release your grip on the light cover so it will hang freely off of the fixture.