Went online to get my 1098-E for 2019 and found out I have a 1098-E for 2018 that I haven't claimed. Can I still claim it and how?

Yes, you can!  You can claim this by filing Form 1040X to amend your 2018 return.  To amend your return, follow these steps:

1. Click on this link to download the correct version of our free amendment software TurboTax 2018 Amendment Software.
2. Install the TurboTax 2018 software on your computer.
3. Sign into your return at TurboTax.com with the user ID and password used to file your 2018 tax return.
4. Look for Your tax returns and documents and click Show
5. Select Download .tax file.  Save this file to a folder where you can easily find it. 
6. Launch the TurboTax program.  If it doesn't automatically detect your file, click on File and then Open Tax Return and then navigate to the folder where you saved your .tax file to select it. 

Now that you have the tax return double-check that it is exactly the same as the return that you filed before proceeding. 

1. As a best practice, save a copy of your tax file.  Use the Save As command (Duplicate if using a Mac) to create a new file with a unique name such as  My 2018 Tax Return Amendment.
2. Follow the instructions on the screen to begin the amendment process.
3. Add the missing student loan interest.
4. Proceed to the Review tab to review the return.
5. Print the return and mail it to the address that prints with the return. 

Note that amended tax returns can only be filed by mail and may take 12-16 weeks to process.  Approximately three weeks after you mail your return, you can track the status on the IRS website here: Where's My Amended Return?