Short answer: choose the photo, pick the 4 × 6 inch sheet and the passport 35 × 45 mm size, and download. Six copies fit at the default 2 mm gap and 3 mm margin; print the PNG at 100% scale, never “fit to page”, or the millimetres stop being true.
Print at 100%, not “fit to page”
A print dialog that scales the image to fill the paper will resize the photos too, and a 35 × 45 mm photo that prints at 38 × 49 mm gets rejected. Set scaling to 100% or “actual size” and the sheet's own margins keep the photos where the form expects them.
What the sheet does not do
It does not crop your face to a head-and-shoulders ratio, brighten a background or remove a shadow. Those change the photograph, not its layout. Crop first, then come here — the result is only as good as the photo you bring.