Hi there!
Without knowing your full health history it could be challenging to actually devise a plan to help you “gain” weight. As a healthcare provider myself I have to first question if there is a medical reason why you aren’t gaining any weight? And also, what things have you already tried in the past to do so?
There are various options to safely doing it such as increasing portion sizes in your daily meals and talking into account things like your metabolic needs, macros, dietary needs etc...things like that.
But an even healthier way to go about it, might be to talk with your actual healthcare provider or a nutritionist (which you might be referred to anyway by your provider). Who could help you to devise a safe and beneficial plan that can help you in the way you desire to be helped.
Best of luck to you on your goals ahead. We are here to support you!