We don't fix things, we're users helping other users.
Is the selfie camera working in the Lenovo camera app? If it is, there's nothing to "fix". You could email the developer of the 3rd party app and ask him to make it work with your phone's selfie camera. Or you could use a 3rd party camera app that lets you control the camera better, and learn how to use the settings. Most selfie cameras aren't known for great dynamic range (which is what your problem is dealing with)
If it doesn't work with the Lenovo camera app, you probably need the front camera module replaced.