1/ NO food for a week.
2/ Then try 1 or 2 pellets. If he does not eat, net the pellets out.
3/ Keep trying.
The key of rule is: PATIENT, PATIENT, PATIENT.....
Normally, this size of fish can't resit after 2 weeks. But if bigger fish, time may take 4 to 6 weeks.
I used to train my XB...