This "how to" covers the dismantling of a door mirror on my 2004 Skoda Octavia Elegance 1.9TDI to replace the built-in indicator repeater.
This is how I did it. I do not guarantee that this will be the correct method for your vehicle and will accept no liability for anything.
1 -Remove the mirror
2 - Remove electric mirror motors
3 -Remove the upper mirror body
4 -Remove the indicator repeater assembly