After creating any personnel tile, click the Hamburger menu in the header of that personnel tile, and select "Add Sub-Tiles".

In the Tile Content Editor, delete the auto-generating image.

After deleting the auto-generating image, click to add a new image, and re-size the tile, and click the "X" in the top left to commit the changes and exit the Tile Content Editor.

After exiting the Tile Content Editor, you will now see the area where you can upload that image from your desktop.