Use a .tdc file similar to the one attached to this article.

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To use the tdc file, please follow these steps below: 

1. Close Tableau Desktop. 
2. Copy the .tdc file attached called 'Redshift_Test_Custom_connection.tdc' into the following folder : C:\Users\username\Documents\My Tableau Repository\Datasources\ 
3. Open Tableau Desktop and try to connect.

Should you need to share it on Tableau Server, please read the following documentation to apply it to Redshift published data sources: Using a .tdc File with Tableau Server.