Simple project C#

Hi all. Please see the attached mockup. I have an app that open a file that contains tags like $1, $2, $3 etc and when I press the "Find and Replace" button the tags on the file are changed by the text in front of the tag. After this open a dialog box to put the file name + extension and where I want to save. BUT I DON'T WANNA THIS. I added the line "Output Folder" that for now do nothing, but I wanna when I press "Find and Replace", the file is automatically saved into the selected "Output Folder" as txt file, with the name of the word in front of the tag $1. I wanna this for today and I know that an expert C# programmer do this in 15min or less.