You have to access your own account and/or print it for yourself using exactly the same account and user ID that you used when you prepared the return.
Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
Or did you use the desktop version of TurboTax? If so, the files are on your own hard drive or any backup device you used like a flash drive.
To get a copy of your previously filed returns prepared with online TurboTax https://ttlc.intuit.com/questions/1900748-how-do-i-get-a-copy-of-a-return-i-filed-in-turbotax-online
@judian You do not say why you want to amend your 2017 return, but unless you had an extension when you filed the 2017 return, you will not be able to get a refund by amending a 2017 return--it is too late.
It would be so simple if you ALWAYS save a PDF and .taxfile of the return to your computer and save them to a thumb drive so you always have access to them if you ever need them ... remember to do so each and every year after you have filed.
SAVE YOUR TAX RETURN !
EVERY year before mid-October you should save a copy of your tax return as a pdf and print a copy of it for your records. That way you will not be searching online frantically when you need it for a lender, FAFSA forms, your next tax return, etc.