If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over with a lower priced edition. Click on Tax Tools on the left side of the program screen while working on the 2018 online tax return. Click on Clear & Start Over.
….or...perhaps you don't consider yourself to be self-employed, but have some cash income or a contract job that requires the SE version. Many people have both a W-2 job and some contract job income work that requires the SE version in order to complete their taxes....the SE version covers both.
If you received a 1099-MISC showing "Non-employee compensation" in Box 7 for work or services that you provided, the IRS considers that to be self-employment income.