I accidentally filed my 2017 taxes for 2018, and am missing some documents too. How dod I "re-do" my 2018 tax returns

Oh no.  You mean you entered 2017 income information using the 2018 software program?  Big mistake.  If the IRS accepted the return, you have to WAIT until the return is processed.  THEN you can amend the return and change the information to your 2018 income information.  You cannot file a 2018 return until then.

WHEN you amend the return, you will have to prepare a Form 1040X which has to be printed, signed and mailed.  It takes the IRS 3-4 months to process an amended return.

https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed?jump_to=answer_3288565

A 1040X cannot be e-filed.  It must be printed and mailed.  It will take about 3-4 months for the IRS to process an amended return.  It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.

Wait about 3 weeks from mailing and you can check the status of your amended return:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions

https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend

https://ttlc.intuit.com/questions/2566895-what-does-it-mean-to-amend-a-return

Meanwhile, if you need to prepare a 2017 return:

Online preparation and e-filing for 2017 is permanently closed.

To file a return for a prior tax year

If you need to prepare a return for 2015, 2016, or 2017 you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

Remember to prepare your state return as well—if you live in a state that has a state income tax.

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/state received the return.

Note:  The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac.  It cannot be used on a mobile device.