I have noticed something incorrect in my CSR. What should I do?
It is impossible to edit any fields once the CSR has been created. You will simply need to generate a new CSR with the correct details?
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?