You wish to go overland from Tehran to Seoul? That would likely not be an overland in the pure meaning of the word; or do you plan to travel through Noth Korea?
Well, yes, overland, and to North Korea, but not across the DMZ...
Iran to Pakistan to China, then into North Korea, back to China and either by ferry or air to South Korea. I know there used to be a China->South Korea ferry but not sure if it is still running.
The real trip is Tehran to Pyongyang overland... but ICN is the closest point to get a SkyTeam return to the US and onward to Europe.