Hello,
I´m confused as to what box you are referring to, if what you need is to change the ¨Output Folder¨ just click on the ¨Browse¨ button on the lower right side and this will open the Windows File Explorer for you so you can choose a folder to save to.
If this is not the issue please try to elaborate more and provide as many details as possible.
You also might want to consider reaching out to NCH technical support for assistance on this.
https://www.nch.com.au/support/index.html 
Good luck!