how do you turn sentences into plain form?
example how would I turn these into plain?

오늘 한국어 수업이 있어요.

바쁘세요?

also what would be the plain form for 네

Question

how do you turn sentences into plain form?
example how would I turn these into plain?

오늘 한국어 수업이 있어요.

바쁘세요?

also what would be the plain form for 네

Answer

You mean like this?
오늘 한국어 수업이 있다

바쁘다 (though I am not sure you can use it to ask questions in that form)

As far as I know(!)  네 is not used in plain form. But I have been wrong before.