Want to add writing credit to Antonio Vivaldi for Concierto Para Mandolina in C Major in Love Potion No. 9, not listed in the credits

Just click the Edit Page button on the bottom of the Soundtracks page.
I recommend you select Correct/Delete so you can see how the existing tracks are formatted.
Then when you're on the page with those tracks, find the drop-down to Add items, and add 1 item.

Based on what you listed above, it would look something like this:

"Concierto Para Mandolina in C Major"
Written by [link=nm0006334]

If you have more info, like who performed it, you'll see other items with such info, and can imitate them.