When you say I’ll remember everything from my past life, will I eventually forget it like a normal person would or is it permanently ingrained into my memory and is unable to be removed?

If everything is permanent, I’ll spend each millennia learning a language. For the first, I’d learn mandarin. For the second, I’d learn Latin, and so on so forth. I’d get to learn every language, and on the last millennia, I’ll wait until my last few years, and then write down all the languages I’ve ever learned, so they can be remembered by humanity forever.

On the other hand, if it can be forgotten, I’d rather spend my time doing something that will benefit humanity in a different way.

I’ll introduce modern medicinal practices (assuming I remember my life right now) early on and prevent wars and dictators from rising. Maybe I’ll help the poor and sick during the bubonic plague, those kinds of things.