Root CAs created outside your DigiCert® On-premises Private CA account can be uploaded with the keys.
Export the root CA and full chain, including the root and keys, in PKCS#12 or .pfx format.
In On-premises Private CA, in the CA Services menu, select Manage CAs > Roots.
Select Import root CA.
Select the Accounts that can use this root CA.
Designate the imported CA to be used for all CA functions or only for revocation checking.
Select the HSM provider and HSM partition to save the keys to. (optional)
Enter the password for the exported root CA file.
Select the exported root CA file.
Select Next. The imported root CA appears in the list.