Allergie requests for P&O

This question is specially for people who have cruised with P&O or are about to. How do you inform them of food allergies? I couldn’t find a specific online form for it. Just a phone number - has anyone called them and they were able to take down the food allergy details? We booked through a travel agent in the US, and even he couldn’t find the link. Whenever we call P&O, they tell us to go through the agent. So we just go round in circles.