This information applies to all versions
Nik HDR Efex can be launched via the File menu's "Export With Preset" option. If you do not see it listed, Lightroom may not have been fully installed before the installation of Nik Collection. If Lightroom was not installed prior to installing Nik HDR Efex, please close Lightroom and run the Nik installer again.
If this wasn't the cause of the problem, the Export settings within Lightroom may not be correctly configured. In Lightroom, go to File, then Export. Next to "Export To," select Nik Collection. Then click the "Add" button under the Preset list, and title the Preset "Nik HDR Efex." Nik HDR Efex will now be available from the Export With Preset menu.
More information about installation can also be found in the user guide.
To view the user guide, please click this link and select the language you prefer.