You must update the ePO - On-prem public DNS name in the console.
ePO - On-prem must be installed on your GCP server.
Select Menu → Configuration → Server Settings.
Select Trellix ePO Server Public DNS from the Setting Categories pane and click Edit.
Enter the Public DNS name and click Save.
Run the query,
update [EPOServerInfo] set RmdSecureHttpPort='443'on the ePO - On-prem database to enable the secured port 443 for ePO - On-prem DNS.
The ePO - On-prem public DNS name is updated, https://<Public DNS NAME>:<port>.