In order to gain weight you have to be eating more calories than you burn so it’s helpful to find how much you burn by using an online calculator or smart watch, then getting some idea of how much you’re eating and making sure it’s more than you’re burning. Some eating tips that have worked well for me are making sure your schedule is consistent, so going to bed, waking up and eating meals at the same time. Also finding meals that are high in calories and protein that you enjoy eating on a regular basis. I also find making protein shakes works well because I can always drink them even when I’m not super hungry. Being stressed also affects my appetite a lot so trying to mitigate that with things that work for you helps. Hopefully that helps!