Identity Manager does not have an out of the box TEWS request sample for Forgotten User ID task. Attached is a document that walks you through the 3 step process to recover the User ID when using TEWS.
Forgotten User ID will need a three step process in order to recover the User ID.
Step 1 - The request will send the user's email and retrieve their security questions.
Step 2 - The request will provide answers to the security questions and retrieve the OID.
Step 3 - The request will provide the OID (received in response 2) to retrieve the actual User ID of the user.
Please note that each subsequent request needs to use the Transaction ID received by its former response in order to continue the session of that same overall task.