My travel conundrum...

I'm travelling, with an Iberia-issued ticket, on the HEL-MAD Finnair-operated service. As it's 4h30 in Y, I'd like to select an exit row but:
- Iberia (web and customer service) can't access the seat map as it's a Finnair service.
- Finnair (web and customer service) can't access the seat map as it's an Iberia ticket.

I've successfully (and gratefully) used the Finnair web to select seats on other OW airlines. Ironically, it seems that I can't use it for their own flights...

Would anyone be able to suggest a workaround? A search of the forum didn't produce any obvious solutions.

Kiitos / Thanks!