How to File an Affidavit of Support. Much confusion surrounds the need to submit I751 affidavits and how to write them.We explain and provide an I-751 affidavit sample. This tip sheet will help you complete Form I864, Affidavit of Support Under Section 864A of the INA. Detailed. Fill in the sponsor's full name, date of birth, and contact information. Specify the relationship to the immigrant. Use our I130 affidavit sample and tips to create a strong affidavit for your spouse. Include these key points and avoid common mistakes. 1. Talk to the person immigrating to the US. The person for whom you write an affidavit should be someone you know very well. The "Affidavit of Support" is a signed document to accept financial responsibility for a family member who is seeking a green card.