I'd just keep trying, maybe you could wiggle the tweezers a bit? My morphs seem to respond to movement, and if I just put something right in front of them, they wont eat it. Mine dont like frozen bloodworms either, but I keep trying! The best thing to do is have patience when trying to feed. Sometimes it takes a while for the newts to "inspect" the food.
Have you tried feeding them anything live that you could just let them hunt in their tank? If you have a pesiticide-fee ("clean") yard, you can look for things like baby woodlice or small slugs. My morphs love hunting them. And it seems to make them "trust" the handfeeding more. But this is only what has happened to me, you might find a better way to do it.