You can't, sorry. :) any eggs that are still little and need to be incubated can just be deleted directly from your inventory. But you don't get any XP when you do it this way, so...
If you touch them with your bare hands then no, because the 'mom' will disown them. It's something to do with the scent of us humans. It's okay if you don't touch them with your hands though unless...
" The mother just rejects the baby after she smells and senses that it has be touched by human hands. So, I wouldn't try to. Just let nature take its natural course. " Actually, this is not true....
If it does not appear to be cracked, there is nothing wrong with putting it back. The mother will not mind the little bit of scent you may leave on the egg. The mother may have pushed it out...
Put you mouse on account (farthest to the right on the bar near top of screen) click edit profile put in your password (in blank underneath your username) then go down to box and put in the code....