Start with some filling and healthy foods that are easy to eat. Yogurt mixed with walnuts or almonds is good, and the nuts have lots of calories for just a tiny portion, but they have the healthy fats so very good for you, as is the yogurt, which is easy to get down if you cant eat. Also try protein shakes that you make in the blender with milk, powder and banana or other fruit. Liquidity things that are high in calories and nutrients will stimulate your appetite. And just start walking for exercise.
My former and future me.