Configuration pages in TWiki are just other pages. If you have sufficient rights to edit the page, you just edit the page as though it were any other TWiki page. The things surrounded by percent symbols indicate variables. Leave a space after that, and the next thing on the line is the value of that variable.

I haven't set up a TWiki in over a year so I'm sure it's changed some, and the specific one you mentioned wasn't familiar to me. But the general layout looks the same.