: Open the resulting .gmap file with Garmin MapManager to register it on your system.
These tutorials provide step-by-step guidance on extracting map archives and installing them onto your GPS device: How to Import TOPO to a Garmin GPS YouTube · ExpertVillage Leaf Group
.img files are intended for direct placement into the /Garmin folder on a GPS device's micro SD card.
: Once extracted, you will typically find a .gmap folder or a .img file.