How to configure SSL for the main domain of proxmox mail gateway?

[vantranvn]

I have read this documentation page before but still cannot configure it.
I now have a certificate to use for PMG and I have uploaded it via the web interface.
What other steps do I need to take now to be able to apply the downloaded certificate to the PMG admin site?

https://pmg.proxmox.com/pmg-docs/pmg-admin-guide.html#pmgconfig_systemconfig