My indicator has stopped working. To replace do I need to remove the glass and take off the back cover?

Yes, as you suggest. There are four small screws once the glass is out to release the lower part of the cover. The indicator is an LED so it may not be the cause of not working.

 

You should be able pull the glass out by moving it to point inwards and then pulling the glass out by putting your fingers behind and pulling. 

That's the theory but mine was so tight I was in danger of breaking the mirror. In the end I gave a new puddle light bulb to the Skoda Garage and asked them to do it as the car was with them for other work.

 

Pull the mirror out as described, switch the relevant indicator on then wiggle the wires going from the indicator housing into the door.  It may just be a bad connector.

Ok I will try that