Hi moe7404 and welcome to LQ!
And sorry I missed the question about Libre Office and actually moved your question over to the Introductions forum.
You may have just lost a shortcut to it and not lost libreoffice. Can you open a terminal prompt and type in "libreoffice" and hit Enter, or Return and see if that loads it. If so, we may have to just re-set up a shortcut.
If you do need to install/re-install:
Mint should have a software manager which is available in the Administration menu. In there you can type into the search box, libreoffice and you should be able to see that package and try to install it.
There are other options with more control and potentially more adjustable results, however let's first try the most fundamental method and then move on to more difficult/advanced methods and see if that gets you the application.