If this is a table of contents macro, the technique is pretty simple. Here’s an example on https://tiddlywiki.com:

- Open the
Contentssidebar menu. - Note that the initial
HelloTheretiddler is already in view. If not, just pick one. - Look at its tags. This one includes
TableOfContents. Click that one. - You get a dropdown of all the items with that tag. Drag the entries up and down to reorder them
- Note that the right-hand menu adjusts with every drop.
That’s all you need to do.
There’s more info in the video. You can open the tag TableOfContents to see that it is indeed being served as a TOC macro. You can note its list field, which has the same ordering information you saw in the dropdown (and on the menu.) If you choose, you can edit this directly rather than dragging and dropping. You can also see the caption field. You can edit this directly to alter the menu title. (In the video, there’s one extra step, since the caption transcludes the text of another tiddler. We look that up under Advanced Search > Shadows)