You can't. The conversion tool is only for proforma from 2018 to 2019. In any case, the tool is not even meant to convert every single data field because the focus is on data that need to be rolled over.
Instead of relying on your client's haphazard input on a DIY return, which you could end up spending more time correcting and diagnosing (even if you could import the data), you may as well just start over with a brand new return.
Still an AllStar