You are unable to have a pop-up of the migration Wizard in order to migrate a client net service account to become a portal user.
Email Security.cloud
Some service accounts may not receive the pop-up Wizard due to some back end issues.
Resetting the account's password once again will clear up the issue and force the account to have the migration pop-up window once again.
Step by step instructions on how to reset can be found in below article:
https://knowledge.broadcom.com/external/article?articleNumber=144158