I'd go to April 1995 and try to ensure that Commodore UK won the bidding to buy the group.
Or I'd go back earlier and try to influence the designers to use standard parts to help make the Amigas cheaper and more easily upgradable e.g. PCI, standard SIMMs etc
Yup. Definitely something like that I had in mind, so we probably could still be buying new C= Amigas these days. Nothing would beat THAT future. And ofcourse some PC-compatible standards included, so Amiga could be still affordable for "the masses".