Cann't enable Cache Reserve in my domain

I want to enable cache reserve because currently data transfer directly from origin source. How can I enable cache reserve setting in my cloudflare.

This is under the CACHING menu for individual zones.

See the full documentation below, including pricing.

Thanks for your reply,

Yes I seen this menu, but what should I do any other setting change?
Because Data transfer still call to origin resource. please kindly check photo.