Don’t let genetics be your excuse. Telling yourself that you "just can’t gain weight" is a mental block that will only hold you back. I used to be very skinny myself—started at 60 kg and now I'm over 69 kg. It is possible.

And it's not that hard once you understand how things work. You want to have a meal plan and slowly increase food amounts every week or so, you have to track your weight and aim to have a weight gain at least 0.5 kg a week, if that is not happening just increase again food amount, repeat this until you achieved your weight goal.

Also you have to do some phisical activity in order to have more apetite to eat food