To avail of senior citizen discounts at restaurants in the Philippines, you typically need to present your senior citizen ID, which serves as proof of your age and eligibility. The discount is usually applied on the total bill, but it may vary by establishment. It's important to ask for the discount before the bill is processed. Additionally, some restaurants may have specific requirements, so it's a good idea to check with them directly or visit the official government website for more details on the guidelines.