Not certain of your age however the best way to put muscle on is “naturally”. I say muscle and not fat. If you are “stuck” the first place to visit is your food plan. What, when and how much are key elements for putting on muscle. Recovery is imperative (sleep, resting proper intervals between sets as well as workouts).
Nutrient dense complex carbs, lean proteins and good fat sources are the best. It’s pretty simple math if you know your lean body mass. Katch/McArdle formula computes your Basil Metabolic Rate (BMR) and your Total Daily Energy Expenditure (TDEE) based on lean body mass then it’s simply a matter of adding more calories in to gain.
Sounds simple but it’s not. If you add too quickly you will gain fat. Consulting a registered dietician is excellent advice so they can guide you through the process. I will leave you with the advice that it’s best to get your nutrients through natural food sources first and foremost. Good luck and continue to train hard.