Hi John,
Right now Overview tool is not part of 64 bit version of MapInfo Pro. We are in discussions to add Overview tool in the next release of MapInfo Pro.
If you have 32 bit version installed, then its Overview tool can be used in new 64 bit version by running 32 bit version "overview.mbx" located @ "installation directory\Tools\overview.mbx" in new 64 bit version.
Once MBX is run in 64 bit version of MapInfo Pro, tool will be available in Home Tab > Tools Extensions > Running tab > Right click on the Overview tool to enable context menus of the tool. You can unloand tool's MBX anytime you want.
Hope it helps.
-Thanks,
Ayush