Copy the /etc/openxpki/config.d/realm/ca-one sample directory tree to a new directory (cp -avr /etc/openxpki/config.d/realm/ca-one /etc/openxpki/config.d/realm/ca-two) within the realm directory.

In /etc/openxpki/config.d/system/realms.yaml, update the following section:

# This is the list of realms in this PKI
# You only need to enable the realms which are visible on the server

ca-one:
    label: Verbose name of this realm
    baseurl: https://pki.example.com/openxpki/

#ca-two:
#    label: Verbose name of this realm
#    baseurl: https://pki.acme.org/openxpki/

# This is the list of realms in this PKI
# You only need to enable the realms which are visible on the server

ca-one:
    label: CA-ONE
    baseurl: https://pki.example.com/openxpki/

ca-two:
    label: CA-TWO
    baseurl: https://pki.example.com/openxpki/

Save the file.