Mix according to directions on the box while also adding the red velvet extract and red dye if using.
Pour into a greased heart shaped oven pan or whatever pan you’re using. 
Place in oven for the amount of time listed on the box for the type of pan you’re using. I went with the 9x9 recommendation for mine and put it in for 27 minutes which ended up a little gooey in the middle so closer to 30 minutes would have been better.
Mix it until it’s fully blended and a good spreadable consistency.
Once cool dollop the cheesecake mix on top of the brownies and spread so it evenly covers the brownies. The red velvet amounts needed will vary based on what kind used. The kind I used had red dye already in it and was more potent than the previous one I had been using so I needed to use less and didn't need any red dye