All SnapMagic parts have slots represented on the Edge.Cuts layer.
To be able to find the real shapes of the slotted holes, please select View > Drawing Mode > Sketch Pads.
Technically, support for these cutouts outlines does not exist in KiCad but it works fine and board manufacturers will understand that this is a cutout in the gerber files.
However, you should tell your board house that the information on the gerber file (containing the Edge.Cuts layer) needs to be milled from the board.