It would help if we knew why your 2018 return was rejected. When it was rejected you received an email that had a rejection code or message. If it was for the most common reason--AGI---that does not matter now, since you needed that to e-file, and e-filing is closed for 2018. A 2018 return can only be filed now by mail. If the rejection was for some other reason, you might still need to fix it before you mail it.
Online tax preparation and e-filing for 2018 returns is now permanently closed. You had until midnight on Tuesday, October 15 to finish and attempt to e-file; if your e-file was rejected you had until October 20 to make corrections and re-file. Now it is too late to use online software or to e-file. If you have any changes/corrections at all to make to your 2018 return, you now have to complete it using desktop software, which you must download to a full PC or Mac (not to a mobile device).Then you need to print, sign and mail it.
If you already paid for your online software you can ask customer support for a download of the desktop software.
They are available from 5 a.m. to 5 p.m. Pacific time Monday-Friday.
If you are getting a refund, there is no penalty for filing late. If you owe tax due, then file and pay the amount due as shown on the Form 1040, but expect a bill later from the IRS for the penalty and interest you will owe. Only the IRS will calculate this—TurboTax will not calculate it.
It sounds like you need a copy of your 2018 tax return to submit to the financial aid office, but you never filed a 2018 return.
As others have said, you can no longer do that with TurboTax online.
To use TT download software (for a fee), see https://ttlc.intuit.com/community/taxes/discussion/access-a-prior-year-return-not-working/01/962519#...
To get free forms from the IRS, see https://www.irs.gov/forms-pubs/prior-year