It is important to note that a factory reset erases all data from your phone. The reason we do factory is basically to bring back the original functions of the device as it were at first when we purchased the phone. This can be done depending on users' expectation.
For an Android device, click here to know how to perform a factory reset.
- For device using Windows Microsoft Operating Systems, click here to know how to perform a factory reset.
With iOS Apple devices, click here for help with factory reset.