For someone of your age/height/weight, you need to be eating around 3500 calories a day to gain 1 lb a week, or around 4k calories to gain 2 lbs a week. If you do any form of exercise, you'll need to eat even more than this.
I would suggest starting off with shakes if you're not used to eating a lot (if you need recipes just let me know), while also gradually increasing the amount of food you eat at each meal. Don't push yourself too hard, but just try to eat like 300 extra calories throughout the day. That could be a granola bar and a glass of whole milk, peanut butter banana sandwich, fruit salad with nuts and greek yogurt, etc.
There will be an adjustment period where you feel full all the time and may become discouraged by the lack of appetite - but in time (one or two months) with consistent overeating, your body will require more food to feel satisfied. Sometimes you just have to push through that hump of being miserable because you're overly full and force yourself to eat even when not hungry. But if you push TOO hard, your body can rebel you you may run into digestive issues.
I'd suggest trying to eat more calorie dense foods - nuts, peanut butter, lots of butter and oil when cooking, carbs (pasta/rice/potatoes/bread, etc), cheeses, whole milk, greek yogurt, granola, etc. It helps to have your favorite foods around at all times and to allow yourself to indulge every single craving you have. Nothing worse than getting a craving and not having any food in the house lol.