When you say that it's coming out in horizontal mode, what do you mean? Are you talking about on the phone or on a PC?
On a phone, you should be able to orient the screen any way you like.
On a PC, the video will always play back with the widest part of the screen at the bottom. That's how video works. If you filmed with the camera on it's side - i.e. the narrowest part of the screen at the bottom - then when the video plays back, it will be on it's side, as you'd expect.
You may be able to find a video editor that will allow you to flip the video on to its side.
