Need to uninstall libre 5.3 and install an older version.
It-don’t-work posts are not helpful in diagnosing problems. You need to provide specifics regarding your system, what you have done, and what is happening.
What operating system?
What was your previous version of LibreOffice?
Who “automatically installed” LO 5.3? An administrator? Have you spoken to them?
Do you have administrative privileges on your computer? If not, that is probably why you cannot un-install LO 5.3.
What happens when you try to open documents?