Where do I enter a 401(k) contribution included in Box 20, Code Z of my K-1 in order to receive the deduction?

Your Schedule K-1 may have been improperly prepared or this amount in box 20 has been provided to you for informational purposes only and is not reportable anywhere on your tax return.  Is this Schedule K-1 from a partnership (Form 1065) or an S corporation (Form 1120S)?  If it's and S corporation, does your W-2 show your elective deferrals in box 12?

It is from a Partnership (Form 1065).

Contributions made to your 401(k) in the partnerships plan should have been reported on the Schedule K-1 (Form 1065) in box 13 with code R.  Contact the preparer of the Schedule K-1 for correction.

Thanks for your help.