To apply for senior citizen discounts at fast food restaurants in the Philippines, you first need to obtain a Senior Citizen ID card from your local government office. Once you have this ID, simply present it when ordering your meal at the restaurant. Most fast food chains and restaurants honour this discount, which is usually around 20%. It's a good idea to check with each specific restaurant for their discount policies and any required documentation. For more detailed information, you can visit the official government website or contact the restaurant directly.