How do I submit my problem with the language not on the list?

I wanna start with easy problems. It wasn’t hard to find where to submit the solution, however, I have no idea how to submit my Kotlin solution. Yeah, I’ve heard on the Twitter that you guy supports Kotlin so I thought could use Kotlin to solve solution.

How can I do that?

I think you are trying to submit the solution in the language which the specific problem does not accept.
Every problem has specific languages in which you can submit the solution. You can see the list of languages at the bottom of the every problem page.

Some problems do not support some languages. If your language isnt available in drop-down menu, then you cannot submit your code in that language.

But I thought CC said on their Twitter that they support Kotlin?