Heifers have small appetites

I have two charolais heifers who need fed up a bit, but can't get them to eat. They just kinda pick at it and walk away. They are going to be my show heifer projects for FFA so I want them to look good. I've had them for a little over a month now and still can't get them really interested in their feed. Wondering how I can get them to have more aggressive appetites.
They're on purina stocker grower

Do they have free choice hay, if so, only feed them hay after you feed their grain, and give them at least 30 minutes before you hay them.

You might want to get some 4 way (wet cobb) and see if they eat that, if they do, slowly mix
the other feed into it, this way they can develope a taste for it.