I needa lose some kgssssssss

I’ve gained SO much weight. Does anybody have any tips that they can give me concerning eating healthy. And how do you stay motivated. I always eat Healthy for a few days then go back. It’s always like one chocolate bar then im back to square one. How do I do it guys I’m so lost. I know I know calorie deficient etc but for those who have lost 15kg+ how did you guys stay motivated and what did you do. I’m looking to lose 20kg. I’m like 84kg rn and I’m 5’8.