We have tried the Delta and AF apps with no luck.
As of today, all I hear from my travel agent, the Delta agents and the Air France agents, is that passengers w/ Delta codeshare to AF can NOT get seat assignments. So it's a `luck of the draw` if you will get a decent seat on the flights and as mentioned above you may have issues getting to your final destination.

Air France has to be the worst in customer service in the industry... And these Air France tickets are NOT cheap tickets. That is, expensive Air France tickets and horrible service. What a way to run an airline...