If you've bought Rapid Resizer, in the step where you enter the size, click on the Download button. You can either download the unsized design file (PNG or SVG) or the resized PDF.
On an Android phone or tablet, your download should end up in the Downloads folder of your Photo, Gallery, or File Manager apps.
There isn't yet a batch download option to get all your designs at once. Let us know if you'd like that.