How to adjust shipping rates

Hi,
I have finally managed to get my product listed on amazon…wooohooo!
however, I would like to offer my buyers free shipping. I understand that this is done from the **Settings>shipping ** route.
however I have no option to input £0.00 as my shipping cost. The product details come up with standard only, with the option to view the shipping rate table.
how can I offer free delivery without going dow the prime/fba route?

kind regards
Muhammad