How to redirect an domain to subdomain?

Hello,
I want to know how can i redirect an domain (example.com) to an subdomain (www.example.com) ?

I use docker bunkerweb-aio and the bunkerweb ui.

I have an service with SERVER_NAME = example.com www.example.com

In Redirect section i have set REDIRECT_FROM = / , REDIRECT_TO = https://www.example.com , REDIRECT_TO_REQUEST_URI = off , REDIRECT_TO_STATUS_CODE = 301

But it’s not work.
Maybe i need to declare an environment variable ? like example.com_REDIRECT_TO=https://www.example.com

Thank you for the help.