You can lose weight by eating only once a day as long as you're not consuming too many calories when you do eat.
However to really lose weight you need to also exercise such as by riding a bicycle, walking, running, hiking, jogging, running on a treadmill, using a rowing machine, exercise bike etc.
When you do the exercise and then only eat once a day then you can lose a lot more weight.
When you don't eat much then your body then turns to the fat in your body to get energy and so your body feeds off your body fat when you're hungry.
So when your not eating and your body starts feeding off your body fat then you lose the weight.
So although eating only once per day can help you lose weight you should also exercise because the exercise makes the weight loss go faster and the exercise also benefits your health as well.