How to have PSConfig forget the farm details and start afresh?

Hi

As my IDX server was down so I removed it using Central Admin on my SharePoint 2010 farm.
Now I am trying to add it back by running PSConfig on IDX server.
BUT it still remembers old farm settings and fails (error: server not part of the farm).
How to have the PSConfig forget its settings so I enter the farm name and config db manually? And then try to rerun which should succeed?

Thanks a lot.