Please refer to the chapter "Restore Tasks" starting from page 33 of the most recent manual. Open the manual from inside the software, don't use a downloaded copy. On page 39 you will find "Restoring from an Isolated Backup Image", on page 40 "Mounting a Backup Image". On the screenshots you will see a tab "Restore from file".

BUT: The linked manual is a little ahead of time. These descriptions are not valid for the actual version 17.4. They will be available in 17.10.X which will show up within the next days. Then HDM 17 will be in a state we supporters are dreaming of since 17.2.3.

Mounting an available backup is already possible, but not the import of an archive created with older software or after loss of the archive database. That's only possible from the WinPE boot medium in 17.4. In the upcoming service pack it will be possible within the running Windows.