How do i proceed with islamic divorce?

Assalamu alaikum, i hope you’re doing well in shaa Allah. I’m considering divorcing my husband as i’ve exhausted all other options in making the relationship work. Alhamdulillah. We are based in the USA, we had nikkah done but didn’t file with the USA Law. How do i proceed with islamic divorce? Do i need witnesses? Do i just tell him i’m divorcing him? What if he doesn’t agree, who do i contact to help? Thank you for you time jazakAllah khayr