On the left hand side menu go to “Products”
When you hover over the word “products” a little grey down arrow appears to the right of the word. Click on that arrow.
A submenu will drop down below.
Then in the tabs across the top, click on “Shipping”.
Then scroll down and in the lower left hover over Flat Rate and when the edit link shows up, click on it and on the right side you will be able to set the shipping.
Then hit update and you are good to go!