First of all, visit the catalog and find the shirt that you want. Then copy the URL id. Next, visit Roblox asset downloader and paste the id at the end of URL and, proceed by pressing the enter button. A file will starts downloading. Then you have to go to your download folder and need to change the file type. After you change the file type, you need to open up Roblox studio then drag the file into the studio. Things will pop-up as a shirt file or pants file.
Next, choose the file you want to insert and go down the temple id and copy the URL. After copying the URL and paste it in the top bar and hit enter. And the next file will start downloading . Visit your download then change the file type to PNG format. And you have the original copy of the shirt or pants.