If you get a new Android smartphone or have connection problems, the connection between the Connected Phone app and your Android device will need to be disconnected.
Open the Connected phone application on your computer. In the left column, go to Settings, select the phone, click the three dots icon next to the device, and then select the Disconnect button. In the window that appears, click Yes to approve the disconnection. The Android phone is now listed as an Inactive device, but in fact, the connection still exists. To remove it completely from the Windows 10 app, you need to delete it from your Microsoft account.
Go to http://account.microsoft.com/devices in your browser and log in with your Microsoft account. Find the device you want to remove and select Show details. Under the device name, select More actions / Remove. Tick the Uninstall this device checkbox, and finally select Uninstall.
Then, once you’re on the Device Manager page, it’s a good idea to look through the list of devices attached to your account and delete any that you no longer use or have, as described above.