Since your goal is to build your chest and upper-body muscle, the focus should be on adequate protein intake, progressive strength training, sufficient calories and recovery rather than simply taking a mass gainer.
Your current diet does provide protein, but it can be improved. Aim for approximately 1.6–2.0 g protein/kg body weight/day, which is roughly 135–170 g protein/day, preferably distributed across 4–5 meals.
You can include protein sources such as eggs, chicken/fish, paneer, curd/Greek yogurt, dal, legumes, soy/tofu and milk. A protein powder is not compulsory if you can meet your requirement through food. However, if your dietary intake is insufficient, a good-quality whey protein can be used as a convenient supplement.(you can initially start with Whey Concentrate Protein Powder of brands like Muscle Blaze, True Basics, Well-being Nutrition, Optimum Nutrition, 1 Scoop a day after your Gym). But make sure you're drinking atleast 4 litres of water daily.
I would not recommend a mass gainer in your case because you already weigh 85 kg at 6 ft and your goal is muscle development rather than simply gaining body weight. Creatine can be useful for strength and muscle performance, but it should ideally be considered after assessing your diet, training routine and medical history.
Next Steps
If you share your complete day's diet, workout routine, your lifestyle, underline medical concerns (if any), only then I can help you calculate your protein requirement and suggest a suitable muscle-gain diet plan.