Express Replacement in UK. What courier is used to send and return back faulty iPhone?

I am wanting to apply for Express Replacement in UK because my iPhone 12 Pro has the yellow screen tint, and I have had enough because I cannot watch shows or TV properly because the screen is not displaying the correct colors.

I want to know what courier does Apple use in UK? If they use Post Office, UPS or Hermes it's fine, but I won't be able to return my faulty iPhone 12 Pro if they use DHL or Fedex.

Please someone advise.