Database
[{_id:ObjectId("5a934e000102030405000000"),CanonicalWebLink:"test/mordu/episodes/try"}]
Query
db.collection.update({CanonicalWebLink:{$regex:"/mordu/episodes/"}},[{$set:{CanonicalWebLink:{$replaceAll:{input:"$CanonicalWebLink",find:"/mordu/episodes/",replacement:"/mordu/webseries/"}}}}],{multi:true})