Per the IRS Instructions for Form 8949, page 5:

Stock acquired on various dates. If you sold a block of stock (or similar property) that was acquired through several different purchases, you may report the sale on one row and enter "VARIOUS" in column (b). However, you still must report the short-term gain or (loss) on the sale on Part I, and the long-term gain or (loss) on Part II.

TaxAct® supports an entry of "VARIOUS" as the date acquired on Form 1099-B. You would enter the data on Form 1099-B in the Investment Income section of TaxAct. Enter "Various" for date acquired, then enter the cost basis, date sold, and sales proceeds. The holding period will be determined based upon the reporting category you select (A-C for short-term; D-F for long-term), if one has already been selected. However, if a reporting category has not already been selected, the program will default to reporting category A, indicating a short-term transaction.  

To enter this information in your TaxAct return:

1. From within your TaxAct return (Online or Desktop) click Federal. On smaller devices, click in the upper left-hand corner, then select Federal.
2. Click Investment Income to expand the section and then click Gain or loss on the sale of investments
3. Click Capital gain or loss (Form 1099-B)
4. Click +Add Form 1099-B to create a new copy of the form or click Review to review a form already created 
5. The program will proceed with the interview questions for you to enter or review the appropriate information