I need to file my 2018 school district tax forms.

You have not said what state you are in, but you cannot prepare or e-file anything for 2018 online now.  Any return for 2018 has to be prepared on paper and then printed, signed and mailed.  It might be  better for you to get the forms from the school district and prepare them by hand.

To finish a prior year return started in TT online:https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS and/or your state received the return.