We need a lot more information then you have given - in particular:
- which software and version you are using.
- are you creating a DVD of BD disc that you want the video to play in a loop?
- what settings are you using ? - a screenshot will help.
If you are wanting to export to, for example, a mp4 video file then you cannot make these loop automatically, this has to be done by the player used to play the movie.