I had to replace the RHS indicator lens as it had a hole in it, and my car is coming up for MOT. It ought to be a simple job since you might also need to replace the bulb. The lens is kept in place by a wire clip that snatches onto a steel member. Problem is that there are coolant pipe work and lots of stuff around, this makes the wire clip virtually inaccessible for anything other than a baby's hand.
To get the thing off I could prise the clip off by pushing a flat bladed screwdriver in from the front. But be careful not pushing the wrong bits; I used a LED torch for this. Getting it back again on was even more difficult. To get a bit of more room, I took off the round plastic cover at the back of the headlight. And now the trick: I made a small hook from a coathanger wire (where would we be without them). Then I could catch the end of the wire clip in front of the pipework and pull the wire clip in place with a satisfying "snap" sound. Pyh!