I’d break up the queso fresco, grind some salt to a powder with a mortar and pestle, add it to the queso fresco and mix together, then put the ball back in some cheese cloth and re-press it. You could probably add a sprinkle of water before putting it in the cloth to help the texture if it’s too crumbly. Queso fresco needs to be salty, otherwise it’s just like dry ricotta.