How to remove a mapped domain

This is the third time that I post this question. Every time that I do, I cannot find it back after while. I will do something wrong for sure.

I have changed the name of my blog to Dutchbaseballhangout.wordpress.com.
But the mapped domain is still yankeebiscuitfansdutchblog.mlblogs.com.

Every time I look at google for the new name, I see this old mapped domain still pop up. How can I get rid of it and replace it with a new one?

Thank you.