How to roll back from Windows 10 Mobile preview to Windows Phone 8.1

Microsoft recently made available a new preview of Windows 10 Mobile (build 10512) through the Fast ring of updates with a bunch of new changes. Although, now more users can get access to Windows 10 Mobile preview and get their hands on the new preview of Word, Excel, PowerPoint, and OneNote, Microsoft warns that there is a significant number of bugs in this particular build for Windows phones, including a bug blocks two-factor authentication.