Download source and open project file (.sln) in Visual Studio or an IDE of your choice. By default the executable will be located at ExcelMultiReplace/bin/Debug/net6.0/, so for testing, add your Excel folder into that location.
If you downloaded the .exe, just move it to any folder you'd like to edit, and double click the exe! Note that it may take up to 10 seconds to open the window. Excel Multi Replace will also perform replacements on all nested folders.
If you downloaded the source, publish the project using Deployment mode = Self-contained and Produce single file checked.
Enjoy!