What is a CSR?
A CSR stands for Certificate Signing Request and is necessary for all SSL certificates in order to complete the generation process. A pair of CSR and private key can be generated from your server.
Here is the online CSR generation tool. This tool generate both CSR and Private key. Using this tool you can change CSR credentials and generate a new CSR and Private key pair.
If you are getting CSR related error on the server please consult this article - CSR can not be decoded error?