@bustytig You are indeed already on an instance!
So my original post there was cross-posted from Twitter, which may explain a lot. :) But also, a lot of people try out other instances before they settle on one they like. For example, witches.town is very customised (different buttons, different terms for things. Each instance has its own admin and it's own rules, atmosphere, style of moderation...
So to move, you just visit the URL and create a new account. A bit like making a new email address.
@cassolotl that makes sense indeed! :D I thought it might have been a cross post but I still went "wait a minute..."