Walmart ESPP

I sold Walmart ESPP in Dec 2024.  My 1099-B tax form has a note for the purchase basis of (transaction details unavailable).  How do I calculate my cost basis.  I do not have the prices per share that I paid.   I purchased the stock that was sold over a period of 6.5 years from Jan 2005- Jun 2011.  This is a FIFO plan.

 

Kimberly