The "Get Windows 10" app not showing in Windows 7 or 8.1 ? Here is the solution.

Step 1: Make sure Windows Update is turned on and downloaded all recommended updates.

Step 2: Just click on http://download.microsoft.com/download/F/2/2/F22D5FDB-59CD-4275-8C95-1BE17BF70B21/GW10Appdiagnostic.diagcab
Link and rest will be done by Windows.. Enjoy !

For more details: https://support.microsoft.com/en-us/kb/3081048