problem with site originally installed at temporary URL

I have a site which I originally installed at https://213.175.206.48/~dealvarn/ which is now running on its permanent URL. Problem is that the site returns an error page if you visit the temporary URL and the temp URL is topping the Google rankings if you search on the organisation’s name.

As you’ll see if you visit the temp URL the error is due to a plugin which isn’t working because the database details were changed when the site was switched to the permanent URL.

Can’t see any way around this – I’d like to be able to put an HTML divert at the temp address or use noindex metatags but don’t think this is possible. Any help would be very welcome.