As I can see in the installation manual, you will need to plug the microSD into the card reader and start the utility on your PC. Then use the File > Install > Navionics Charts. The software requires an original ScanNav cartridge (SD Card or other storage device) but if the microSD has the same folder structure, from the window the opened select the drive with the charts and click Install.
If this operation is not working, then try and copy manually the charts from your microSD Navionics folder to the installation folder on the PC.