Checkbox extra field

Hi,
I need an extra field in the checkbox called ‘Download file’ where admin can add download file URL https://i.ibb.co/bvRCqW1/download-file.png. When customer purchase product with selected variation and complete order process then the file will added to customer account https://i.ibb.co/2yZw7zJ/file-purchase.png

The page I need help with: [log in to see the link]