How to correctly bulk? Advice?

VividVegan

I lost a lot of weight and inches and looked great for a while but now I'm starting to get too thin up top and I know spot reducing is a myth. My only problem area is my glutes/bottom. I still hold almost all of my body fat there. Even my most recent DEXA scan confirmed so. Losing more weight is too risky because my body keeps choosing everywhere except the glutes despite weight training, squats, and high protein consumption. I was recommended a bulk before doing another cut, however I wasn't told how exactly a bulk works. Can someone please explain? I'm currently 5'7 and 125-128 lb. My measurements are 32-23-34. Waist is getting too thin for my comfort and chest is close to flat. I do still have my very slight abs but glutes are not solid and its getting annoying. I even have sag lines since they aren't toned. They are the only things that aren't toned. Any bulking advice?