Here is a great explanation about how you use Visual Studios merge tool to merge files: https://roadtoalm.com/2013/10/22/use-visual-studio-as-your-diff-and-merging-tool-for-local-files/
You can find of plenty other tools for compare and merge on the Internet, but you probably already have a Visual Studio license. Here is an overview of other tools: https://en.wikipedia.org/wiki/Comparison_of_file_comparison_tools
