How to gain 5kgs in 3 months?

hi.some people have body tendency in which even if they eat 100 pizzas they`ll not get fat.so maybe its ur tendency.but dont worry.u can have banana along with milk.to increase weight u have to have them together,u can eat chicken,mutton,eggs,paneer,cheese,potato… too much)but everything should be healthy.i hope i helped and best of luck.