Most people, if they could time travel, would go back and buy stock in a successful company or kill Hitler, or otherwise try to right some wrong. Or they would be terrified to interfere at all, I guess.
But if archivists went back in time, we wouldn't do any of that. We'd just go back and tell people to write dates on things.* Or to label their photos. Or to actually write stuff down! Or to keep things!
Scene: Eliza Hamilton is getting ready to burn all her letters. Fwoosh, a time traveler appears. "Eliza, wait! Don't do it! That is an important historical record and someday everyone is going to want to know what is in here!"
Okay, in fairness, I actually kind of support Eliza Hamilton burning her letters. They were her business, and she has a right to her privacy. So, bad example. But in the case of my however-many-greats-grandfather, I would definitely do some intervention. Like, get the guy to write down who his parents were, and his wife's name (with the right spelling, because we aren't sure and that's really causing problems).
Scene: Joseph, probably out working on a farm? Fwoosh, time-traveling archivist (myself). "Joseph, what's up? I've got some paper here, I just have a couple of questions. Who are your parents? Excellent. Oh, I can meet them? Great. Siblings? Perfect. And your wife, is she around? Okay, great. Let's just write down all this info, and keep it safe so I can find it in a couple hundred years. Yeah, that will be nice."
The Spaniards who burned Aztec records? Definitely visiting them. The millions and millions of old photos of who knows who? Fix that. Maybe pop by and put a word in with Madison and his buddies to clarify some of the punctuation in the Constitution (can you imagine if all of the confusion around the 2nd amendment is really an ink drop or something?).
Not to say that stopping Hitler isn't a noble cause or anything. I get it. But if I get access to a time machine, I'll be fixing the historical record.** You're welcome.