To use senior citizen discounts when booking a hotel in the Philippines, you should first ensure that the hotel is accredited to offer such discounts under the law. When making a reservation, mention your eligibility as a senior citizen and provide your valid Senior Citizen ID upon check-in. It's a good idea to research hotels beforehand or call ahead to confirm that they participate in the senior discount program. For further clarity, check the official website of the Department of Social Welfare and Development or the hotel’s own site to understand their specific policies.