hey manish,
unfortunately currently such an option doesn't exist. if editing is an important feature perhaps you might want to disable comments and go with the native replies instead? with replies (also for the main question itself) editing is already working fine.

if that's not a solution for you and you need the comment editing part feel free to submit your feature request to our voices section at http://stackideas.com/voices instead of the forum as that's the place we're monitoring when it comes to planning for feature implementation in upcoming versions.

have a nice day