Question

How to access previously filed tax returns when I am the joint person on the returns?

I am the joint person on the filed returns needing access

Employee

You will need the username and password. How to Access prior year online returns
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/27010

If you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online. So you need to make and keep your own backups.

Or request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript

Or get a copy of your return using form 4506
https://www.irs.gov/pub/irs-pdf/f4506.pdf