Keep putting it in, and change it to a sweet aromatic sweet like mango or banana. Use Kevlar or Dyneema protected fingers to give the treat that way. Knit gloves work for iguana bites because their teeth are arranged like opposing knife blades, which the yarn stops, unlike what is needed to protect from peg-like teeth. Look for inexpensive knife-handling gloves. And sleeves with thumb-holes. You put the sleeves on over the gloves to hold the gloves on when the iguana is clawing.
Doing that is normal for an ig who is still resisting being tamed. But it qualifies as unneeded stress. Can you avoid coming close to his enclosure during your own daily routines? Does he have a large enough hide that he can feel unseen when he's in it? He knows when part of his tail is showing.