I need to file for tax 2017 and 2018. How and where?

You cannot use TurboTax Online to file for past years. TurboTax Online is only for the current tax year, which is now 2020. To file for earlier years you have to use the CD or download TurboTax software for each year that you need. You can purchase downloads at the following link. There is no free filing for past years.

Past Years' Products

You might get a better price from a reputable online seller that still has TurboTax in stock for the years that you need.

Tax returns for past years cannot be e-filed. You will have to print your past-year tax returns, sign them, and file them by mail. Mail each year in a separate envelope. The IRS stopped processing mailed tax returns for several months because of the Covid-19 pandemic. They have started to process them again, but they have limited staff and a huge backlog, so it will be quite a while before your past-year tax returns are processed.