Keep in mind that this particular help system may not have been created using RoboHelp.
If you want an alphabet index, it can only happen in WebHelp output. Assuming you are creating that output, double-click the Single Source Layout and click Next twice. Choose Pure HTML as your output option and generate.
Thank you, that worked. However, the -SEARCH- field at the top right had corner of my online help no longer displays. Is there a way to have both alphabet display in the Index and the -SEARCH- field to display in the top right hand corner of online help?