There are two ways you can do it.
First and safest is take them to a local shop and ask to put them on the boot heaters. Look for the most laid back guy and you probably won't get charged. The second way is to stick a blow dryer to them. But don't stick it in them because it could melt the liner. Just heat up the inside as best you can. Making sure not to forget the toes. My recommendation would be a shop even if they charged you a little. But its your call. Good luck.