Reverting files back to open with "unknown application'

[Guest]

I accidently changed a file to open with a different application, and now I
need to change it back so that it's an unknown file. I've gone through the
"Properties" section, but there doesn't seem to be an option that lets you go
back, or select "unknown".

Many thanks for your help!

 

[SingaporeWebDesign]

Hello,

Start > Control Panel > Folder Options > File Types (tab) > delete as
necessary

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Singapore Web Design
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Singapore Web Hosting
http://www.bootstrike.com/WinXP/faq.html
Windows XP FAQ

 

[niytot]

I also just changed a file that is supposed to open with an unknown application unknowingly to excel. Now I want to revert it. I have tried the solution above but do not know what to delete.
Please can you guide me on what to delete