Denise D on chat helped a lot. The help page "Use QuickSend to Resend a Campaign Email" is clear, but seems incomplete. It has a 3-step get-started item, and then ends. For duffers like me, the rest of the steps would be helpful. Such as... 4. [After selecting the contact(s)] Use the More Actions pull-down.
5. Choose QuickSend
6. From the pull-down list, choose the message you want and click SEND.