I've noticed that kibble builds tarter etc up on there teeth and I'm not too keen on feeding it anymore so was wondering what the best food would be to trasnition him over to it he really likes mince but I very rarely give them that due to the fatness so would could I use to start the transition and could someone give me a diet plan
Fattier cuts of meats are actually better for ferrets (eg. dark meat vs light), as that's what gives them energy. If it really concerns you or your ferret is a bit overweight, you can offer leaner meats, eg. ground/minced turkey or chicken. I assume when you say mince, you mean regular ground beef. You can totally use that if he already eats it, though it may be a bit tougher to transition using beef, as it tends to be stronger in taste and smell than other proteins.. but it could work out just fine if he already enjoys eating it in ground form.
Or you could go the soup route if you really struggle.