How to take kidfix size base off back (temporarily!) -awful diagram included

[Butterpaneer]

Hi all, I wonder if anyone can help - I've actually had this issue with our kidfix size seat, and was sent a video by the company we bought it from showing how to fix it but the links has expired and I can't remember how to do it! This is for my mum's car seat.

So the back bit won't stay upright or recline slightly to be flush with the seat of the car, whenn it should. The issue is that there is a plastic bit on each on the the base which are ironically supposed to limit the seatback falling forward by stopping two similar plastic bits on the back from moving past a certain point . However, the seat has been incorrectly assembled such that the bits on the back are in front of, rather than behind, the base clips.

I've attached a terrible drawing to try to explain as the plastic is black and difficult to take a picture of... Anyone have any ideas?

Tia!

Can you also add a reference image of the seat where it's difficult to see the bits, so I can see where these clips are? The diagram is helpful, I just can't picture where it is in the seat itself.

My assumption based on how they tend to come into the shop is that if you push it so it's fully lying flat (this might involve pushing it past a point that makes it click, which feels horrible) you should be able to detach the backrest. Then that might allow you to reattach it properly. But since it involves pushing it to a point where it feels like you'll break it, I am not sure about suggesting it if it might be currently assembled incorrectly.

If all else fails I'd email Britax directly and ask for the video again because I expect they will still have a copy of it. The retailer might too.