If I sold stock that I received from rolling over my 401k (distribution was taxed at the time), how do I calculate the capital gains and report it on my taxes?

When I tried to roll over the 401k to my new employer, the cash value rolled to an IRA without tax penalties, but the stock transferred to a brokerage account where it stayed for approximately 2 years. I did pay the taxes on the stock value at that time. I don't seen an option to select for how I received the stock, and would I treat it as I purchased the stock for the price at distribution for the purpose of calculating cost basis? The form 1099-B has boxes 1b, 1e and 2 blank.