Filling my Betterment through TurboTax. 10099-B Long Term, has "various" in box 1C but Turbotax wants a date. What to do?

"Various" is a valid entry, and TurboTax should accept it.  If the program will not accept it, then use one of the dates from the transactions that are being reported.  Just be sure you are using a date that makes the transaction long term.