If you are talking an old ZTE Blade then they only have one camera. There would be no reversing, as when doing that it isn't changing which direction your phone's camera is going, but switching over to an alternate camera. On devices that have more than one camera.
Now if you are talking a newer ZTE Blade (there are a few Blade versions) and it has the dual camera, then the option to change which camera you are accessing is in the camera screen itself.
Once inside the camera app, click on the settings within that app (not the phone's settings) and there should be the option to switch between the cameras in there.