Finally some feed back on this one.
After landing reverse was selected on all 4 engines.No big beal there.
Nos 1,2,3 ENGINES went into reverse,(green)NO 4 DID NOT.Capt attempted to recycle no 4 engine,instead accidently hit TOGA.The rest is history.a/c fully left the runway.The a/c is still in Seoul.
Am told a serious amount of damage on all 4 engine.etc