Hye,
Thanks for the query.
You are underweight for your height.
Initially you need to gain healthy weight to maintain stamina and energy.
Firstly understand that weight gain is very dependent on genetics and metabolism along with your daily diet and exercise routine.
It is important to know that just eating just two heavy meals a day will not help.
Weight gain is all about taking more calories than you burn. Eating the right foods at the right time is very important. There is no one food that helps weight gain.
Eat meals at frequent intervals. You need to eat at least 6 main and mid meals a day.
Eat a mid meal between each main meal.
Avoid junk foods.
Include dairy, eggs, nuts, fruits, dry fruits, starchy vegetables, rice, bread, whole grain cereals, smoothies, masala milk, ghee, cream in your meals.
Just eating sugary, sweet foods is not good. Try to have healthy deserts like kheer, chikki or lassi.
Avoid alcohol and smoking.
Exercise at least thrice a week. It helps development of muscle mass and improves appetite.
Even if you were to take just medicines or supplements they will not work in isolation. You need to have a calorie and nutrient dense meal and good exercise routine, it's crucial.
Do not start your day with tea. Do not skip breakfast or delay breakfast in the morning.
Eat a healthy breakfast within 30 minutes of waking up. If that is not possible then do not have tea to start the day. Have milk fruits or nuts. And then breakfast after 1 hour is fine.