Thank you
How old is your mata mata ??
I got 3 of my mata mata at a very small size.
In the beginning I feed them live fish, after they get settled i stop leaving live fish in their tank, instead once in a few days I catch a live fish in tongs and feed. In the beginning they take time to understand that it's food in the tongs, so you gotta be patient.
Once they associate the tongs with food, every time you bring the tongs they will strike each time you hold something in the tongs.
Although they strike they might not readily accept new foods, my fimbriatus is a brat and will regurgitate tilapia. Here's a video of rejecting tilapia
It's a slow process but will work eventually.
I have never trained a large specimen, as I see that as they grow larger they get more and more shy and nocturnal.