For an ESPP sale, my 1099-B lists MULTIPLE for the date acquired in box 1b. TurboTax does not accept this. It wants a specific date. What should I do?

I don't know what TurboTax will accept. Many shares were purchased over many dates. I have a 1099-B that summarizes the purchase and sale, and I am stumped. The 1099-B does not provide a date acquired as a summary; it just lists "MULTIPLE".