Creating Custom Thumbnails: Overcoming Background Skin Upload Challenges

I want to use my bg skin for making thumbnails but we can't download it, and if we can't download it , we can't upload it on prisma app , I used screenshot but it shows up laying on the floor , i want a 3d character, so that can give them a pose and use other tools to make it attractive, so the main problem is how should I upload my bg skin , the photos below are my inspiration...