Hi,

there are a few things you can do with a snake that isn't used to frozen mice/rats. Since snakes use their eyes and their noses to detect food, you should make sure that the mouse smells like a live mouse (sometimes you have to put them in some substrate for rodents, so they smell like it). The mouse should be warm and should move a little bit when you offer it to your snake. Some live earters nevers accept frozen food and others do without no problem. There are also cases in which a snake that eats frozen mice will decide to only eat live from this point on.
My ball python also ate live when I got him. The breeder told me that he's a very good eater so he'd probably eat the frozen mice. The first time I tried to feed him, he refused but that was because he was still stressed from the new environment. The second time he took the F/T.
If you want to switch a ball python from live to frozen, you have to be patient and you have to feed live if you're snake does not accept frozen mice.

I hope this was at least a bit helpful.