Database
[{test:1,"accountCreation":[{"startDateTime":"","endDateTime":"","isDone":"Yes",another:1},{"startDateTime":"","endDateTime":"","isDone":"Yes",another:2},{"startDateTime":"","endDateTime":"",another:3}]},{test2:2,test3:3}]
Query
db.collection.update({"accountCreation.isDone":{"$exists":true}},{"$unset":{"accountCreation.$[x].isDone":true}},{arrayFilters:[{"x.isDone":{$exists:true}}],multi:true})