I'm not sure where you're having the trouble so I'll break this down very simple for you,
You'll probably want a computer, as it typically is easier to navigate files on a computer rather than a tablet. Also some computers do not recognize the portable as a usb device. I can confirm that computers running Windows 10 or Ubuntu (Linux) will work. I haven't been able to get my MacBook to recognize the device once it's built but maybe someone has. There is no guarantee that a tablet will recognize the usb in the portable, so even if you are able to format the usb correctly so that the Wii recognizes it, you will have to take apart the portable any time you want to edit the contents in storage (games, VC, Channels, etc.), and the usb in the Ashida is not very easily accessible as it is somewhat covered by the main motherboard.
The files can be downloaded by clicking the link on the original post that says Ashida Optimized Files. A zipped "rar" file will then be downloaded. You will have to unzip that file. Most computers now have included software that will do so, but if yours does not you can download a free unzipping program, such as 7zip or WinRAR. From the newly unzipped file you will need to navigate the directories to find the files. The easiest path is probably Ashida Optimised > Main Body SLA (PCBWay Compatible) > Ashida Front (or Ashida Back). The front and back files are the ones you are going to need to upload to PCBWay.
When navigating to PCBWay, you will see some tabs near the top of the screen. One of them says "CNC | 3D Printing." If you hover on that tab, a drop down menu will appear where you can select "3D Printing." On that screen, you should see "+ Select CAD Files." Select and drag the Ashida Front and Ashida Back files to that spot in the window and they will begin to upload. It may take some time depending on your internet connection, but eventually they will upload and you will be able to choose the material and color from the options they have available. On the right hand side, once you have finished uploading and choosing materials, there will be a large green button that says "Submit Request." Press that when you want to submit your files for review. When they pass, they will begin printing and then be shipped to you.
I echo everyone else thus far by saying you have a long road ahead of you. I assure you that our intentions are purely benign when we say this. You will need to study very closely a lot of material before you are going to be able to attempt your first portable. I would suggest the following material, since things can be a little bit difficult to find at times to newcomers:
Good luck, we wish you the best. Remember that when it comes to your equipment buy nice or buy twice. I think I can speak for us all when I say we hope it turns out good for you.