gmap kmz mac transfer

Hi, I have downloaded onto my MacBook Pro (OS 10.14.6) two tiles that captures parts of Columbia I am interested in. They are downloaded in the gmap format. When I try to change the format to kmz so that it will work on my Garmin 64s the download is changed into a gmz file folder with 4 items. This makes it unusable on the Garmin. What am I doing wrong? How do I make an effective transfer? Thanks, Tom