if you have an SSL cert provided by an cert authroity. Assuming that CSR was generated outside of the controller , all you need to do is to merge the certificate file (.crt) with the private key using a text editor. The order should be
crt followed by private key
-----BEGIN CERTIFICATE-----
** Certificate content ****
-----END CERTIFICATE----------BEGIN RSA PRIVATE KEY-----
** Private key content
-----END RSA PRIVATE KEY-----
Once you save this merged content as .crt file you can upload it to with PEM certificate type and passphrase. The controller will accept the certificate even though it has own CSR. This option can be used to copy to multiple controllers.