How do you get into the WTF or ITF (world taekwondo federation) and (international taekwondo federation)?

I don't know about ITF.

In WTF, the short answer is join a WTF-affiliated school.

The long answer is that your test must be seen by 3 or more 5th dans or higher. Kukkiwon expects forms, sparring, breaking, and essays to be presented. The quality of each is at the discretion of the 3 or more committee witnesses. You fill out paper work, do your techniques, pay the instructors the $150 or so (plus expenses to the 3 committee members), submit your application by way of the committee, and you should be good to go in about 3-5 months.

Who do you train under? You may have your black belt, but it may not be under the larger umbrella organization. You are trying to get into an organization without and instructor? You are still a beginner in the martial arts. Most of the time you trainer a dojang affiliated with a larger organization. Talk to your teacher, friend.