The amount on Schedule K-1 Box 13 Code AF is carried over to Form 3800, Part I Line 1 and further described in Part III for Form 8881, Part II. You don't need to enter this credit anywhere else on your return. Note that this is a non-refundable credit, so you must have tax due on Form 1040 Line 16.
The IRS Shareholder's Instructions for Schedule K-1 (Tip) indicate that if the only source of a credit on Form 3800 is a partnership, S-Corp, estate, or trust, you aren't required to complete the applicable credit form (in this case Form 8881). Instead, the credit is added to Part III on Form 3800 with the EIN of the entity from which the credit arose.
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