Well, you could ask the lemmy repost bot to make reposts of all of the subs you’ve posted here, on Lemmy, but ot only takes posts from today and maybe a few days back, reposts them here, and than just carries on reposting from that point on. It doesn’t actually repost retroactively.
Though you could probably speak to the dev that actually runs that instance, maybe he can make a bot mod that does the same, but with users and does it retroactively. It’s worth a shot IMO 🤷.