Well firstly, I would start a cult around my immortality, at first something small like a group of friends and converted strangers, then slowly expanding over the next 1,000 years, with demonstrations of power and endurance, such as drinking Instant Death Poison, surviving several public assassination attempts some of which i would hire after the first dozen or so failed attempts just to make it extra clear i can't be killed. After my following becomes strong enough, I will take on the courts and governments of the world, secretly causing WWIII or something similar to clear up land/lower the population of people not loyal to me. I will then be free to install my own theocratic/autocratic global regime, in which i'll actually try to effectively protect and govern my country of between 500,000 and 1 million people as well as keep them happy and personally fulfilled. Then have scientists research advanced medical techniques, more efficient renewable energy (as well as slowly phase out more harmful industrial practices and coal/natural gas usage), and eventually space travel, wherein I'll take my small regime to the cosmos in a self-sustained paradise, while those who opposed my rule will sit on their little rock, fighting amongst themselves, until the sun swallows the planet whole. Then I'd chill and maybe catch up on my 1,000 year backlog of shows, vidya, and dank memes. When I'd get bored, I'd let my paradise descend into a degenerate orgy which I'd secretly be part of and "save humanity from it's sin" by teaching them not to be degenerate. I'd probably get bored after that, so I might start a war with some ayy lmaos or something if I start really running out of ideas.