You don’t actually need a “Dell ISO.” A standard Microsoft Windows 10 ISO will work perfectly on a Dell computer, as long as you install the correct edition (Home or Pro) that matches your license.
Historically, a "Dell ISO" meant a standard Windows ISO that Dell had modified. It included specific drivers for the model (audio, video, chipset) and often pre-installed software like Dell SupportAssist, McAfee, or Dell Update. dell windows 10 oem iso download