While the Eurostar train itself terminates at Midi, your ticket to Brussels is valid to any other train station in Brussels and there are direct trains from Midi to Central every few minutes, taking about 4 mins. When you come down from the Eurostar into either the main concourse or "connection corridor" look for monitors showing the next departures (départs) and for a train going to e.g. Brussels Airport or Antwerp (or even, as long as it's IC and not Thalys, Amsterdam): for all domestic trains going north, the next stop will be Gare centrale, you just identify one leaving in 5-10 mins, go to the platform number given (Eurostar is 1-2, Thalys 3-6 so it could be any number above 7) and go to that platform, where you will find an indicator at the bottom of the escalator and overhead, on the platform, telling you what the next train is (also announcements but you may not understand those). When it comes in, just jump on the train and show your Eurostar ticket to an inspector on board, if asked.
Thanks so much for the detailed response! I appreciate it. I do hope I'll be able to find my way haha thanks :)
That's great, thanks!