You have the disc image. Now what? You have three primary options:
You will be prompted to enter a valid Windows 8.1 product key. download windows 8.1 disc image -iso file- - microsoft
Microsoft previously offered a “Media Creation Tool” for Windows 8.1, similar to Windows 10’s tool. That tool is no longer hosted or supported by Microsoft. Any third-party website offering a “Windows 8.1 Media Creation Tool” is likely unsafe. Avoid downloading executables from unofficial sources. You have the disc image