Hi and welcome to the community.
So you became a Grade 4, flying on Expert server, without being on this Community? Joining the community is not a must, but it does make me wonder where and how you learned all there is to know.
It’s great you want to become an IFATC. But, since your here now, why not first spend time understanding this community, familiarize yourself with the Pilot and ATC tutorials, view the YouTube clips for pilots and IFATC (see posts above). Read the ATC manual.
Become a good pilot first; give way to others, don’t taxi at ridiculous speed, know when to turn on your strobes, know how to approach an airport via downwind, know how to exit across a parallel runway and how to transition through an airspace. Stuff like that.
Then, with that knowledge, first become a good controller on Training Server. Serve the pilots on TS, build your experience and your Operations.
Then, with that experience, start an ATC tracking thread, to get good feedback from experienced pilots, and build on your experience.
Then, after some controlling, you apply for your IFATC, and there will be a good chance you pass.
The journey towards IFATC matters.
Have fun!