To enrol in PhilHealth as a senior citizen, start by gathering necessary documents, such as proof of age like a birth certificate or senior citizen ID. Visit your nearest PhilHealth office or apply online through their website. Fill out the Member Registration Form and submit it along with your documents. Ensure that you receive a PhilHealth ID once your application is processed, as this will allow you to access benefits. For more detailed guidance, it may be helpful to check the official PhilHealth website or consult with their representatives.