How to I update the path to a moved git-svn remote branch

I have been using git and git-svn for a while now but we have moved out svn repository server to another location. So what i am wondering is what to I need to do for git to look at the new remote path so i can continue like before. I have tried changing the url in config to look at the new repo but then when i try git svn rebase I just get :

Unable to determine upstream SVN information from working tree history

The svn repo is exactly the same but has just moved locations to another url.

Thanks in advance.

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