I feed roughly 50% protein(boiled chicken/eggs, earthworms, roaches, crickets, f/t pinkies, etc), 30% fruit, with the remaining 20% being a fairly even split between veggies, greens, fungi. In order to get them to eat a varied diet it's easiest to just dice everything up and mix it together. I recommend earthworms for an animal still settling in. Chopped up worms will continue wiggling for a while and seldom fail to get a box turtle's attention.

These are naturally seclusive animals and it could take a while before yours is comfortable enough to come out and start eating in your presence. They're also largely crepuscular so offer food in the early morning or late evening. They do best in heavily planted, outdoor enclosures and require a fair bit more space than one might guess from their size.

Best of luck and please share pictures when you get a chance.