If didn't file my 2018 taxes and I got a letter from the irs saying please file immediate by 4/12 what do I do. I did a rough draft said I was getting 700 never fina

If didn't file my 2018 taxes and I got a letter from the irs saying please file immediate by 4/12 what do I do. I did a rough draft in 2018 said I was getting 700 qnd I never finalized