Are you using the CD/download? You do not "log on". You open up the program from your own hard drive. Then click "File>Open Tax Return
If you do not know which one is which--it is up to you to figure that out--no one else can see the returns you worked on. Name your returns when you save them so you will know which is which.
https://ttlc.intuit.com/questions/1901659-find-your-tax-data-file-in-mac
https://ttlc.intuit.com/questions/1900721-find-your-tax-data-file-tax-file-in-windows
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