You can only file your W-2 for the tax year in which it was earned. Thus a W-2 from 2017 must be filed on your 2017 taxes. A W-2 from 2018 must be filed on your 2018 taxes, etc. Prior-year taxes can not be filed online; you will need to buy or download the appropriate CD or software.
Please see this website on how to file your taxes for the appropriate year before 2019 (2018, 2017 or 2016).
you must use the software for the year of the W-2. for 2017 and 2018 online preparation and e-filing is closed for those years so you must download the desktop sofware for each year. if you used the online software for those years you can dowload the .tax2017 and .tax2018 files. the 2017 w-2 must be entered in the 2017 return and the 2018 must be entered in the 2018 return. if they were entered in the 2019 return they must be deleted. the 2017 and 18 returns must be mailed. follow TT filing instructions carefully and be sure to attach the proper copy of the w-2 to the return. if your state has an income tax, you must also file those by mail. when filing by mail use a method whereby you can either track them or get proof of deleviery. do not mail 2017 and 2018 in the same envelope.