Can't drag file from Quarantine Manager to Custom Scan list (so can't do manual cleanup)

V 9.5.4, Mac V10.11.6 (El Capitan)

I have several files in the QM which say manual cleanup is required.  Help instructions, page "Add a custom scan of a threat" says in part:

In Quarantine Manager, do one of the following:
In the list of threats, select the threats that you want to add to a new custom scan.
Drag the selected threats to a blank space in the Custom Scans list.

On the page titled "Scans" there already is a custom scan listed, saying, "no items in scan, scan never done, no files with detections."  I double click and a box opens with the scan name and an empty file list.  I can't drag anything from the QM into this box.

In QM, I can highlight only one treat.  The file will not drag into the Custom Scans list, or anywhere for that manner.

Also, that same help instruction page went on to mention dragging files from the "Threat Details box,"  but help had no words about this.  How do I access the Threat Details box?  Double clicking from the QM list has no effect on anything, and there is no context menu when I minor-finger click on one of the files.