Step one is making good choices in terms of eating foods rich in nutrients, I think you’re off to an excellent start there. The next step would be ensure you’re getting the right amount of food in the correct macronutrient proportions. I personally shoot for around 2,000 daily calories with a 50% Carbohydrate 30% Protein 20% Fat split. I’d make a food diary for a week of everything you eat. Don’t try to change anything, just record everything that goes in your mouth. Then use MyFitnessPal to estimate your average daily intake and how you’re getting it. Then use some online calculators to figure out a good daily intake for you to make sure you’re fueling your training properly. Lastly, make changes to your diet to meet your macronutrient or volume goals.
The process is the same as trying to lose weight, but you would aim to just meet your daily balance. A detailed post of the above process is in the link below.