Intermediate CAs created outside your DigiCert® On-premises Private CA account can be uploaded with the roots and keys.
Export the intermediate 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 > Intermediates.
Select Import intermediate CA.
Select the Accounts that can use this intermediate CA.
Select the HSM provider and HSM partition to save the keys to. (optional)
Enter the password for the exported intermediate CA file.
Select the exported intermediate CA file.
Select Next. The imported intermediate CA appears in the list.