If what you're searching for is how to restore your LibreOffice to its original look with the old Toolbar layout, then follow this steps:
Click on the upper left icon of LibreOffice.
A menu will appear, choose the option "Menubar".
With this you can enable the old menu
Toolbar Layout -->
After choosing that option, you will recover your old LibreOffice.
Finally, you can press ALT+F12, this will open the "Options" menu, where you can disable the "experimental features".
NOTE: If you're using Groupedbar Full Ribbon Layout, see the image below, it's easier, just move to the left the LibreOffice Window and expand it, then you will see the other buttons:
Hope this helps, good luck!