How to enable Tracked 24/48 on Amazon

Hi,

I currently sell on Amazon FBM and ebay. Ship with mainly Royal mail.

For some orders I do 48 TRACKED on ebay for large letter, but i cannot find a way to do tracked on amazon. It only shows untracked and signed.

How do i enable tracked 48/24 as i could buy it on royal mail click and drop but not directly on amazon.

would appriciate any help