Here's a partial answer. To learn how to file an amended return for 2017, click this link:
https://ttlc.intuit.com/questions/4252204-how-do-i-amend-my-2017-turbotax-online-return
or if you have a Turbo Tax CD - this one:
https://ttlc.intuit.com/questions/4251801-how-do-i-amend-my-2017-return-in-the-turbotax-cd-download-...
I don't know if there is a charge to e-file. Probably free for Fed, with a charge for state. But if you don't want to pay an e-filing charge, print the amended return(s) and mail, using snail mail. You can always begin the e-file process and then back-out if you see a fee that you don't want to pay.
