You’ll need to sign up for a new account on the other instance. I’d recommend you persevere with getting a lemmy.world one and use that as your main one. Keep the one you’ve got in case of an lemmy.world outage.

Content is generally shared amongst the main instances so you’ll generally be able to see the same stuff wherever you create an account. Most of the Lemmy apps have multi-account functionality so you can add both.