Importing a Private Key
To import a Private Key:
In the side menu, click System Settings.
On the Certificates page, click Import.
On the Import Certificate or Private Key dialog, for the Type, select Private Key + Certificate Pair.

Import Private Key Dialog
Enter the password for the private key.
To update your security certificate, drag and drop or click Browse and select the new Certificate and Private Key, and optionally an Intermediate Certificate Bundle file.
Click Apply.
On the Certificates page, the newly imported files are added to the list. Click in the Active column to activate the certificate.
Click Reboot.