You can't transfer tax data or entries from one tax year to another.

If you must:

1. Opens two instances of PTO, one for the 2020 return you just prepared in error and the other for a new 2019 return;

2. In the 2020 return, filter for input screens that have entries; and

3. Copy the entries, one by one, from each screen of the 2020 return and paste them into the same input screens of the 2019 return.

You'd be the judge of whether this can save you time.