Hello, I am filing the final 2020 1065 partnership return (2 partners) and one partner sold her share (50%) to the other partner (my client). I don't know how to put this sale in the final 1065 tax return.

Besides, she sold her share in Dec 2019 but the previous tax preparer did not file the final return 1065 for the 2019 tax period. Do I have to file the final 1065 return for the 2020  short tax period? if yes, do I have to file the sole proprietor for my client for the 2020 tax period? 

What should I do to convert from partnership to sole proprietor?