[{"_id":{"$oid":"637c1064a2f047f5ab75ac42"},"title":"this is a list","todo":[{"completed":false,"description":"a normal task"},{"completed":false,"description":"this is another task"},{"completed":false,"description":"another task"}],"username":"lucas","__v":3}]

db.collection.update({"todo.description":"a normal task"},{"$set":{"todo.$.description":"new description"}})