Simple. Just drag and drop to the SD card of your gps as shown in the agenda.
Not so simple.
I found this when I tried it:
The single file of a route in BaseCamp is split into 2 different files on the SD card named 'route' and 'waypoints'. No relation in name to the original file. When a second route is copied, it is also split. But now it's 'route0' and 'waypoint0'. And a third copy becomes 'route1' and 'waypoints1'. The agenda does not address this.
What a frikkin nightmare of a file system this has turned out to be. I've yet to be able to figure it out. I still can't alter a route and save it as a different route- BaseCamp automatically saves it by changing all copies of it no matter how many different lists or list folders it's in. Any ideas of how to make it stop doing this? If I'm working in List Folder and List 'Temp" and 'Temp", why does BaseCamp change a file in a totally different List Folder? The only way I've found is to
never, ever leave any files in the BaseCamp lists! Export each and every file to somewhere else- I use a folder in 'My Documents'- then completely remove/delete it from BaseCamp. If I don't, and I want to alter a route, BaseCamp changes them all. Yes, even if you have a route named 'route' and copy it so you have 'route1' BaseCamp will change route1 to match whatever changes you make to the original file 'route' if both are contained in the BaseCamp file system.
Again, what a frikkin nightmare of a file system this has turned out to be.