I wish we could wave a magic wand and get exactly as we wish, but that surely is not the case!
Your weight loss has shown on your face even though you say you have not starved yourself but have chosen nutritious food over fatty and sugary foods. Therefore, the change in diet plus the additional 6-8 kms you were doing had to tell somewhere, so it showed on your face. This may be due to the loss of fat accumulated under the skin. You can tone it by some simple exercises like excessive smiling, making an O with your mouth but there are no specific exercises to build muscles in this area.
Now that you are doing 4kms only, that will maintain your weight until you bring in another change in calorie intake or calorie spending.
Keep on with your sensible program and you will start looking better in the face and feeling healthier.