There's only one thing that comes to mind, with any urgency at least, when I think of what I would do with a time machine...
My dad was born in a literal mud hut in one of the most historically impoverished regions of the world. He was the first person in my paternal bloodline to ever get educated. Both of his parents, who died before I was born, were uneducated and illiterate. Totally illiterate. Could not even write their own names.
After reading lessons, when my dad's 6 siblings were helping with farm duties, my dad would come home and share with his dad (my grandpa) what was taught at school that day. Eventually, motivated by my grandpa's deteriorating health, my dad slowly taught his dad how to read.
Sometimes, when I feel like half-assing a class assignment, or basically any time I feel lazy, I think about that simple fact. My father...taught his father...how to read.
If I had a time machine I would just go and sit there. See my grandfather who my dad speaks so highly of. Watch my dad teach him how to read.
People don't realize how good they have it today, in the information age.
They concern themselves with the GRADE they get, instead of the INFORMATION they learn.
They want stuff GIVEN to them, instead of FIGHTING for it.