In some fta boxes this job is done Automatically like if you forget to fill Ku parameters:9750 to 10600 in LNB selection and suppose you put C band details like: 5150 then it will convert all your ku band frequencies to C band.
Note : Actually what happens the box try to read according to details fill in the lnb setup so the conversion happen automatically. If not you can do manually by filling details as above..