From The Document Foundation Wiki
How can I make a slide show run in a continuous loop?
First, all the transitions and animations in the slide show must be automatic. When that is done, do the following to have the slides loop continuously:
- In ▸ ▸ , select Loop and repeat after and input a delay, if you wish.
- The screen will be black during the delay. If you wish to display the LibreOffice logo on the black screen, check the Show logo option
- Confirm with OK.