100 Dolorosa Room 123 San Antonio, TX 78205 Phone: 210-335-2678 Fax: 210-335-3998 Monday - Friday AM - 5: Here's a step-by-step process for how to write an affidavit whether you need a short or long-form template.How to Fill Out an Affidavit. When Do You Need a Notarized Affidavit?