I have no idea what to do about eggs but I fear if they are stuck to the walls above the water line it's probably to late for them. I think for koi breeding they usually use mops or nets or something like underwater grass to catch and hold the eggs so I guess if you want your koi to successfully breed you might need to do some more research to be prepared next time.
Has the water cleared back up? Is there still foam? I would have figured green stuff around the water line might be an algae bloom. If everything is cleared back up then it might just have been the results of mating. But I'd still do some water tests anyway.
There are tons of Koi forums I'm sure so a bit of internet searching should find you more info that you will know what to do with.