1. Open the tab that holds the setting and find its row.
2. Click the value in the Value column (empty values show Click to set).
3. For text settings an input box appears with the current text selected; for dropdown settings a searchable list opens.
4. Press the orange check button to save, or the X button (or Esc) to cancel.

The value is written immediately — there is no separate Save button and no page reload. If you leave a text field empty and confirm, the empty value is stored as the setting's value.