Training a muscle is training a muscle. You can maintain and keep the muscle that you have, increase muscle mass, or lose it. Muscle responds to stimuli, whether you are maintaining or gaining.
The concept of “toning” isn’t really a thing ...well, kind of, but not really.
Toning is a blend of concepts: maintaining or adding muscle mass while decreasing body fat to reveal that muscle.
Exercise while adapting nutrition to lose weight, is the difference between losing weight (muscle, water and fat) and losing fat. Reducing total body fat while maintaining shape is likely the goal you actually have in mind.
Your exercise progam should include strength training. Not only will proper strength training help you keep the muscle you already have, but strength training (any training for that matter that requires extra energy) will burn Calories. Not only that, by pushing your body during the workout, strength training can cause the afterburn effect.