If you want to do it the "right" way, you should use a lua script outside of the game to load the savevars file and export it into the required form from there.
A short search on google
shows that there is a library that allows you to create excel files from lua, which should make this rather easy.
But in the end it depends on what you plan to do. If you want to use it for an addon, it will probably be more user friendly if you just write your own program and don't force users to install a lua interpreter.
Regardless of the method you choose, you will need to
1) somehow get the data out of the game client (-> saved variables)
2) read the exported data (-> anything that can read files will do)
3) parse it (-> depends on how you structured the data before you exported it)
4) put it wherever you want to have it (-> excel)