If you've bought Rapid Resizer, in the step where you enter a size, click on the Download button. You can either download the unsized design file (PNG or SVG) or the resized PDF.

If you have the Designer or Pro version, there's also a Download button when you click on a design in the row of saved designs here.

On an Android phone or tablet, your download should end up in the Downloads folder of your Photo, Gallery, or File Manager apps.