I just install blackarch on top of arch following the steps given on the blackarch website.
You mean the ones where they tell you to pipe a curl command into a root shell to blindly run as root a random untrusted and poorly written script that you've never even looked at? Congrats on finishing your first penetration test: you failed, your system has been penetrated.
You could step through whatever script you downloaded and try to undo anything it has done, but I'm not sure it'd be worth it.
Forget black arch, learn something useful:
http://www.catb.org/~esr/faqs/hacker-howto.html
Thanks!
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