How do i delete multiple files except a single file in it.

If you already have the folder path you could run getFiles on the folder object and then run a loop over the returned array of paths deleting all the files that does not match your name criteria. I have created a code snippet based on mask function of getFiles, it should also work. I have not tested it but you can get an idea of what i am proposing as a solution, to tweak it if needed

function findFiles(f)
{
    if(f.displayName != "c.mxf")
    {
          f.remove()
          return true
    }
    return false
}
var f = new Folder("Path to your export folder")
var delFilePathList = f.getFiles(findFiles)

-Manan