As there is no Insider Hub on Windows 10 Technical Preview for Windows Phone yet, if you run into an issue with the OS, you need to let Microsoft know what they need to fix. In order to contact Microsoft without the Insider Hub, you only have two options (for now). By pressing the volume down button and power key simultaneously, you will launch the Windows Feedback app. You can also open the Windows Feedback app from the Settings list.
When you use the hardware buttons to open the Windows Feedback app, the app opens right to the section where you experienced the bug. So if you are trying to send a text message and your run into a bug, you can press volume down and the power button and the Windows Feedback app will open to the Text Messaging section, making it easier to look at Text Messaging-specific feedback content or submit your own feedback.
As with Windows 10 for PCs, feedback is important for the development of Windows 10 on Windows Phone. If there is something you want to see in a certain features, or if there is something you don’t like about Windows 10 on Windows Phone, this is the best way to let Microsoft know.
Further reading: Microsoft, Windows 10, Windows Feedback, Windows Phone
