Hit Save to send to viewer window.
Go to the Users/Qualifier Editor if you need to add a player for the drop-down.
The "Promote to Current Match" button will clear out current match and move next match into the current match slot, with Auto-Save.
The "Swap with Next Next Match" button is similar, but instead swaps Next and Next Next (useful if your players for Next are unable to come up soon).
If you end up needing the latter a lot, you may want to give the Advanced Matches Editor a spin.
*More matches have been created, but they can only be viewed/edited in the Advanced Matches Editor.
Making changes using this editor does not affect advanced match data.