When you have the files in Garmin connect open each gpx file (called “courses” in Garmin terminology. You will find the list of courses hidden in the “More” menu (three dots) and then in “Training and Planning” then “Courses”. Open each in turn (each will show a small scale map) and click the Send to Garmin icon which is a small blue arrow pointinf at a watch. Then you need to connect your Garmin to the PC by bluetooth or cable. It will show connected in the home menu of the Connect app. Then you just need to activate the “Synch”. On my iPad it takes a while and looks like nothing is happening but eventually the “courses” will appear on the Garmin.