As to changing destination country, you may be in luck calling KLM instead.
I had a flight to Belgium booked in the summer of 2021 which I needed to change to one to Spain instead with different destination and departure airports (ALC/VLC), and there was no way to do it online.
the agent on the phone did it for me at the time.
worth to note, 2021 was still all about flexibility in travel and I didn't have to pay any fees to change the ticket. This obviously isn't the case any longer, so my situation then may not be representative for how it is now.