Adobe doesn’t provide us in Lightroom with a template for borderless prints. It’s not too much of a problem, it’s only a matter of having the right settings. For 4 by 6 inch prints:
File -> Page Setup: set the printer to 4x6 paper. The borderless paper.
Print Module -> Layout Engineon the right panel.
Layout -> Margins: set all to 0
Layout -> Page grid: set the Row: 1, and the Column: 1
Layout -> Cell size: set the Height: 4 inches, and the Width: 6 inches