Switching can be as easy as one feeding and as hard as months of trying.
Tough love is key in most cases but of course this require your snakes to be an appropriated weight.
Easiest way to get started is to switch a a rat the same size than the mouse previously offered (size can be intimidated), once the animal east 3 to 5 rat consecutively you can up the size as needed.
It can take months and during that time do not feed mice otherwise you start all from zero again.
Most will switch even if it take time but be prepared that some may never will. (rare)