To edit track metadata, right-click on the track you want to edit and select 'Edit Track Info' or click on the 'I' icon above the track's waveform.
This will take you to a new view containing all track metadata from rating to tonality. Empty fields will show a '-' giving a clearer view of what is missing from the metadata.
To begin making changes, click into a field or make a change. Once completed hit Done to confirm your changes.