Custom Regions in 3D Maps - Bodies of Water

I am looking for a way to plot data from oceanic regions (and other bodies of water) in 3D Maps (Excel - Microsoft Office Professional Plus 2016, Version 1812). I cannot find any .kml files that contain this information in order to upload a Custom Region, nor do I know how to create a .kml file for this purpose. Are there any resources that someone could direct me to in order to make bodies of water into Custom Regions? Thanks!