ww.wp.xz.cn account does not exist and exist issue

it says the account already exists

Does it? In other words, does an account exist?

Then why do you want to create another account? You should not create multiple accounts https://ww.wp.xz.cn/support/guidelines/#do-not-create-multiple-accounts-sockpuppets

Here there is no any option to change the username.

I am sorry Usernames (your login ID) cannot be changed on this site

However, you can, as you know, change your display name with this link https://ww.wp.xz.cn/support/users/naurej/edit/

If you like, you can register a new account with that new user ID but let us know in this topic and we’ll ban the old account once your new one is created.

You will not be able to use the old email address and will need a new email address for the new account.