I'm not that experienced with WordPress but recently as a task I was given a broken WordPress page in order to fix it. By googling the problem, it seems like a plugin problem. However, I'm afraid that I might break the whole site if I do something wrong (because of my inexperiencity) and moreover, this is a live site, up and running, fully hosted, not in a staging status. So, is there some way to make changes, test the error and try to fix it without making changes on the live site? Is there some kind of a test environment, sandbox or whatever?

If it needs to get downloaded, note that I'm running Ubuntu 18.04. Thank you in advance