If you pulled the trigger on Windows Phone from Windows 10 Technical Preview 2 for Phones a bit too quickly and wish you could go back to your previous Windows Phone OS version, no worries: Microsoft provides this capability via a downloadable utility. Here’s how it works.
Curiously, it’s not a phone reset, which I assume will just bring you back to Windows 10 Technical Preview 2 for Phones. Instead, you must use a PC-based downloadable utility called the Windows Phone Recovery Tool to return to Windows Phone 8.1. Here is a direct download link.
After installing it, just run the Windows Phone Recovery Tool. It features a delightful Zune-like user interface.
As prompted, connect your phone to the PC. (If it was already connected, disconnect and reconnect.)
Then, select it and follow the wizard-based process to return to your previous OS.
If anything goes wrong, don’t forget that you can also use the Lumia Software Recovery Tool—here is a direct download link—as well. As you can see, this also offers to recover to the same build. (Note, however, that the Lumia Software Recovery Tool is for Lumia smart phones only, whereas the Windows Phone Recovery Tool should work for all Windows Phones.)