Dont try to soon, wait a week, if you keep constantly trying to feed them they could get scared and go off feed. In my experience braining f/t with ball pythons doesnt work, scenting them does also if you are thawing them out in water and the feeders fur gets damp the snake doesnt like that sometimes so try letting the feeder dry out.

I let my feeders thaw out all day in the snake room, no hot water just let them sit out. This prescents the room and the feeders dry out from being all iced up.