Main Street Lending Improvement Act of 2020 This bill revises the Main Street Lending Program, a Federal Reserve lending facility established to provide COVID-19 (i.e., coronavirus disease 2019) related business loans. Specifically, the bill (1) allows financial institutions to collect interest on the entirety of certain smaller loans if a participation in the loan is sold to the special purpose vehicle established under the program, and (2) requires the Federal Reserve Bank of Boston to establish a help line to address lender-specific questions. The special purpose vehicle must purchase 99% of the interest in a loan participation originated by certain financial institutions. Additionally, certain financial institutions must receive automatic preapproval for loans under the program.