Things that I'd 100% do if I had a time machine and could only travel to the past:
Tell Ray Blanchards mother to get an abortion so that his evil doesn't pollute the trans community
Tell Emperor Frederick III of Germany to quite smoking because he's gonna get cancer and die 99 days into his reign but DON'T tell him that proto-Hitler will try to pull a coup on him and is actively grooming his son (let him and the powers of Europe sort it out themselves)
Engineer the French Revolution so it results in a liberal constitutional Monarchy built on Enlightenment ideal instead of... That and also help Poland pass the 3rd May Constitution so that it stays independent and allied with the French Constitutional Monarchy. For good measure make sure that Napoleon goes off to work as a mercenary/advisor within the Ottoman Empire and helps their military modernize.
Give the Northwest Confederacy and Musokgee state a bunch of repeating rifles and a mountain of ammunition for no reason dawg.
Hand Jai Singh II of Jaipur a modern telescope and mountains of Textbooks on classical Electromagnetism, Einsteins theories of Relativity, Quantum Mechanics and Quantum Field Theory then tell him to pass them off as his own discoveries
Make sure that Carlos II of Spain has a son or else has a surrogate through me, thus avoiding the War of Spanish Succession.
Tell Prince Shah Shuja of the Mughal Empire that he's sitting on a mountain of Coal and Metal in Bengal (and that the entire Bengal, Odisha and Chhota Nagpur belt basically has infinite metal and energy), explain to him what Coal is, how you can make Iron with it and why it's way better than Charcoal, tell him that he should invest in a navy instead of making the Europeans do everything and also that European style line infantry and standing armies are the way of the future.
Give Timur the Lame cannons and tell him that he should go for Constantinople while the Ottomans are down instead of aiming for China.
Give the Mesoamericans paper to write on and also make sure that the Mesoamerican method of making Rubber is never forgotten.
Let God sort out the mess of butterflies and Paradoxes I just caused.
(NOTE: I AM NOT DOING THIS BECAUSE I THINK IT WOULD LEAD TO A BETTER WORLD BUT PURELY BECAUSE IT WOULD BE FUNNY)
