Can you explain step by step how you have done it? :) If you change to CSR and key in the request to self-generated, it still says username already exists. on

Can you explain step by step how you have done it? :) If you change to CSR and key in the request to self-generated, it still says username already exists. on the other side, if I create my own certificate using custom CSR and key, I still cannot sign it with website CA (taken from original p12 file) since I do not have the private key.