You can let a small piece of banana sit out to attract fruit flies. Not a long term solution, but an easy way to try a different food item.
Ultimately, it will eat frozen food once it figures out it is the same thing as live food. There are likely many tricks to weaning animals from live to dead food, but one simple technique is to feed some live and some frozen food at the same time, so that the animal eats both and thus figures out how tasty dead food is. Every salamander I've met has a much smaller brain than stomach, so this shouldn't be difficult.
