I need to access 2017 return but i have already filed 2018 return somewhere else. how can pay for plus so i can access previous return? this process is unnecessary.

You could also request a transcript of your 2017 return from the IRS if you don't need to see the actual return: <a rel="nofollow" target="_blank" href="https://www.irs.gov/individuals/get-transcript">https://www.irs.gov/individuals/get-transcript</a>

The following TurboTax FAQ can walk you through purchasing Plus and accessing your previous return: https://ttlc.intuit.com/replies/7362231