Flyscreen catch

The plastic catch that secures the flyscreen on our 05 Nuevo side windows (Seitz S5) has broken off.  I have sourced a replacement part, but am finding it difficult to work out how to fit it.  I naively assumed it would just clip in, but it seems it has to be slid in from the end on the blind.  How do I get to this? I have seen exploded parts diagrams but they don't help in understanding disassembly.

We have a similar problem on the small rooflight over the end kitchen. The spring on the catch has popped out and I can't see how to remove the catch so that I can reinsert the spring. It's not possible been to do this while standing below the rooflight. Anybody managed this? Thanks

Here's a photo of the catch