Usually it should be https://www.appextremes.com/apps/Conga/PointMerge.aspx, which I think is what's listed in the documentation. You could also use https://www.appextremes.com/apps/Conga/PM.aspx, which seems to work the same except that it doesn't do the multi-select (SelectTemplates=1). I noticed that when trying to modify a single template selection screen to add the multi-select... caused some head scratching before I saw the PM.aspx at the end.
Note that PM.aspx is the page redirected to even when you start with PointMerge.aspx. Not sure if there's an advantage of using PM.aspx directly.