Use
https://www.google.com/mymaps (Google My Maps). Locate the desired map/route that you would like to transfer. Click the ... three vertical line of dots shown to the right of the selected route, then choose "Export to KML". Save this file do your desktop, open Google Earth, then choose "File\Open" from the top drop down menu in Google Earth... Browse to your new KML (.kml) file on your desktop, then click Open. Your route will now be added to the "Temporary Places" found under My Places.