If I had 20k+ of tuition expenses in 2017 as a full time student that I never deducted on any tax return, can I deduct those expenses on my 2019 tax returns when I file?

[Critter]

No ... if you have 2017 expenses then you must amend the 2017 return ... you cannot just add them to the 2019 return ... the IRS will reject it.

[xmasbaby0]

And as for getting education credit on your 2017 return, if you were someone else's dependent, then the person who could claim you as a dependent is the one who can get the education credit.  If you were claimed as a dependent on someone else's return, that person needs to amend and get the education credit.  If you could not be claimed as someone's dependent for 2017, then you can prepare an amended return to seek the credit.

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

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-q...

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