How do I rotate my video?
This is caused by the camera not reading the sensor properly. It typically happens if the sensor in your phone doesn't register that the phone was rotated before recording or if the phone was flipped after starting recording.
You'll need to rotate the videos in a video editor, re-export them, and upload them to Zubtitle again.
If you're not using a video editor, I recommend using Handbrake: https://handbrake.fr/
It's a great, free video encoding tool. You'll need to make sure to change the settings for the video to rotate it on export: