MITI letter how?

Cannot. 1st june onwards only kementerian level punya letter can use. No more Miti/Co letter.

Say you’re a teacher, then need to get surat from Kementerian Pelajaran Malaysia (KPM)

If you’re JKR engineer, need surat from Kementerian Kerja Raya

If you’re a nurse, need surat from Kementerian Kesihatan Malaysia (KKM)

And the lists go on.

If you keja kilang swasta, i think Ministry of International Trade and Industry (MITI), not sure not valid anymore?

It just sounds logical, but whether the ministries are prepared is another story lol
Depends on your services. What do you do?

Then yours should be manufacturing which is under Miti.