Firstly, I'd ensure the client is fully aware that we have an allergy-free option available for them. Then, I'd confirm the specific allergens they are sensitive to. Afterward, I'd check our product range and identify any items containing those allergens. If necessary, I would consult with my suppliers and look for alternative products that are free from these allergens. Once I have found a suitable alternative, I would make sure it meets all safety standards and is as effective in treating the client's desired concern. Lastly, I would ensure to inform our staff about the client’s allergy so they can take appropriate measures while serving them during their visit to our spa.