I just did this the other night. You have to remove the corner lens (carefully - the tabs holding it in place get brittle as they age, and if (when?) they break, you need a new lens. The lens has to come out as there is another screw holding the trim piece in place under the headlight. One at each end. The plate under the headlight has a rubber lip on the back as well. Once both screws are removed, rotate the grill side of the plate away from the front of the car to about 45 degrees, then slide the fender side of the plate out, exposing the bottom of the headlight.
Before you remove the lens, carefully remove the rubber gasket that goes across the grill and bottom of the lens. The rubber has tabs that go through the lens rim holding it in place. It helps to slightly stretch these tabs so they clear the lens holes. The fender edge of the rubber has a molded rubber hook that curves around the bottom fender side of the lens, which must be pulled towards the fender to clear.
You will need 2 long, thin screw drivers to remove the lens. As Glen says, if not done carefully, you risk breaking the tabs, so you may want to remove the headlight to take the lens off. It can be done on the car if you are very careful and don't try to force anything.
The bottom of the lens looks like the top: 2 plastic clips on the bottom holding it on and 2 on the top. GENTLY pry up the 2 sides of each clip so that it clears the tab on the headlight housing. This can be done by sliding the flat of the screw drivers under the tab, and rotating them so that the blade acts as a lever, raising the tab. The bottom ones are done the same, but if the headlight is on the car you have to work by feel, and the clips have to be approached from the sides (screwdrivers held under the lens and parallel to the lens face.) It does work, it just takes time and care.
Once all 4 clips are removed, the lens is free, but you aren't done yet. there are 4 fat plastic pins on the lens corners that go into guide holes. The pin closest to the lower fender side of the lens doesn't clear easily. Gently rotate the grill side of the lens out from the headlight until those pins clear. Then rotate the top of the lens slightly down until the upper fender pin clears. Finally, rotate the lens slowly clockwise and out from the car until the 4th pin clears.
Reassembly is the reverse of above. It sounds more complex than it is. The hardest part of re-assembly is after the bottom lens tabs are secured, pushing the top of the lens against the rubber seal enough so the top tabs re-engage. Use a folded towel to protect the lens and your hand.
When re-installing the turn indicator lens assembly, make sure it 'clicks' into place, and try pushing it out from behind to make sure it is locked in, or else you might loose it on the freeway!
Good luck, about a 1 hour job.
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