[{name:"name",email:"email",conversation:[{message:"Hi",seenBy:"karen"},{message:"Hi",seenBy:"leo"},{message:"Goodbye",seenBy:"mark"}]},{name:"name",email:"email",conversation:[{message:"Hi",seenBy:"karen"},{message:"Listen",seenBy:"leo"},{message:"Sit",seenBy:"mark"},{message:"Hi",seenBy:"mark"}]}]

db.collection.update({conversation:{$elemMatch:{message:"Hi"}}},{$set:{"conversation.$[c].message":"Hello"}},{multi:true,arrayFilters:[{"c.message":"Hi"}]})