My employer has 401(a) defined benefit retirement plan for me. No where on my W2 is there an indication of what I have contributed to that account. What do I do?

Turbo Tax asks me to get the contribution from my year end statement.  the year end statement from my employer reports the balance from July one year, to June the next year.  Turbo tax asks to indicate my contributions thru April 15 on that tax year.  Am I to estimate what the amount would have been reported spanning January to December of that tax year?  Is Turbo Tax asking if I choose to ADD to my Year End Summary for that Tax year?