So took it to service and turns out it’s a simple fix, no tools req’d to do it yourself — simply release the seat back, fold flat, return to upright and voila. I actually almost tried this before taking it in but didn’t as thought it might make it worse.
I’m kinda suspecting that my 6-yr old grandson may have caused that by releasing the seat belt and letting it fly retracted, rather than gradually releasing. But regardless, now you know how to correct this!