You need to calculate Total Daily Energy Expenditure (TDEE) which is basically maintenance calories. TDEE outside of major exercise like lifting for 90 minutes is composed of TEF, BMR, and LLA. To find BMR (basal metabolic rate) plug in the formula (10*weight in kg) + (6.2*height in cm)-161. This is how many calories you need to sustain your bodyweight while doing absolutely nothing. Next take that number and multiply by 1.2 which roughly accounts for the thermic effect of food (TEF) and low level activity (LLA). Now once you have that number multiply it by .75 and eat that many calories a day while getting adequate sleep and 2g of protein per kg of bodyweight. You can track all that with a calorie tracking app, I use Cronometer (it's free, if it's confusing look up a youtube tutorial). Keep going until you lose your desired weight loss goal of 10kg. Hope this helps! Let me know if you have any questions.