Im buying a desktop version to file my taxes since Im filing late. How can I access my prior year returns which I ve filed on Web?

If your prior returns are locked then you must upgrade to PLUS & pay for the PLUS upgrade to unlock them... however this can ONLY be done when the ONLINE system is operational.  Right now the system is down while it gets transitioned to the 2019 version ... this blackout period happens every year. 

Purchasing the current year software does not give you access to the prior year online tax returns.  You have to upgrade the online account to access those tax returns.

You will not be able to upgrade to the Plus edition for tax year 2018 since the TurboTax online editions for 2018 have closed to make way for the 2019 online editions.  Once the 2019 online editions become available in December, at that time you can start a 2019 return and upgrade to Plus.

In TurboTax Free Edition, you can purchase PLUS to unlock your prior-year .tax file.

The exact instructions will vary depending on the status of your 2019 TurboTax Online return (select one):

• I haven't started a 2019 return yet
• I started a 2019 return but haven't filed it yet
• I've already filed my 2019 return

However, since you have purchased the 2018 desktop edition you should contact TurboTax support and speak to an agent to see if they will let you access  the 2018 online account and download the tax data file at no charge.

Support is open from 5am to 5pm Pacific time, Monday thru Friday

Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/