Unable to customize email content

Description:

Hi
i'm using version 3.9.1
in documentation at this link https://docs.rocket.chat/guides/administrator-guides/email/editing-emails-content

way to change content of email has written
but i can't see **Custom option ** for change to true

please help to solve the issue

Steps to reproduce:

1. Go to administration
2. select Email
3. for example of edit content, i select Forgot password
4. i can't see custom option for set to true
5. see this link -> https://postimg.cc/tYn3NQY3

Expected behavior:

Actual behavior:

Server Setup Information:

• Version of Rocket.Chat Server: 3.9.1
• Operating System: debian
• Deployment Method: docker
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version:

Client Setup Information

• Desktop App or Browser Version: Firefox latest
• Operating System: Win 10

Additional context

Relevant logs:

No source files or tests are named. Start by reproducing the Administration > Email > Forgot password flow on Rocket.Chat 3.9.1 and compare it with the linked email-editing documentation. Done means the documented customization control is available or the issue is clearly identified as a documentation/version mismatch.