When using a mobile device to record video, the screen rotation settings will affect the video's orientation- and your video may upload sideways or upside-down. If your device's screen is locked in portrait mode, your device will not be able to adjust to landscape mode while recording, even if you turn your device. Whenever you're recording a video, make sure that the screen rotation lock is turned off. This will allow you to orient your device into landscape mode and record your video successfully.
Videos and photos taken on smartphones, tablets, and some cameras can look great on your device but appear upside down or sideways when uploaded because the device stores the image's orientation in the EXIF metadata and not all software can read the metadata.
Using an iPhone or iPad:
Swipe up from the bottom of the screen to reveal the Control Center and tap the lock icon to unlock it if it is set to locked mode. If you have an iPad with a Side Switch, turn the Side Switch off to unlock your screen. Visit the Apple support page here which explains this in further detail.
Using an Android phone or tablet:
Open your device settings and scroll to the Display. From there, select Auto-rotate screen to enable screen rotation. Please visit the Android website here for more information.