Push the mirror housing all the way forward and look up under the hinge joint area. There's a small phillips head screw to remove. Then push the inside edge of the mirror glass in so that you have a little access behind the mirror glass from the outside edge. Behind the glass, on the floor of the mirror housing you'll see a springed retainer up through a hole in the floor of the housing. Take a long flat blade screw driver and compress that so that it can pass back through the hole and pull down on the blinker housing. It will just pull down away from the mirror housing. You'll see two light bulb sockets there. A quarter twist releases them. The bulbs are 921's . You can find them at any autoparts store.
-Mike
Phillips head retaining screw ....
Springed retainer clip behind mirror glass in housing floor ....