A high testosterone level is usually not related to your diet. Although eating enough quality protein can maintain healthy testosterone levels, it is very, very unlikely that a high protein diet would contribute to abnormally high levels of testosterone.
There is likely another underlying reason for your high testosterone, and this should be addressed by your physician if it has not already. You still want to consume high quality protein in your day, and your Gainful protein powder won't affect your body any differently than consuming protein-rich foods.
FYI: if you are pregnant, nursing, or have any medical conditions, double check with your physician before starting Gainful or any other supplement.