hai,
i appreciate your concern.
it seems your BMI indicates under weight.
First eat protein nourished foods like Almond,cashew,channa,soyabean,peanut in your daily food intake.
Add jaggery,black gram,and dal prepared with ghee.
take diary product like milk,yogurt,chesse,butter etc. Add banana and tuber vegetables.
take ice creams and fat bound foods.
if you are a non vegetarian take meat and sea food alternate days.

This will nourish in a healthy way and gain weight.

thank you
hope i answered your query