Chord markers are edited in the same way as Section markers, so refer to The Section Track if needed.
Edit the Chord Name
The dialog used to edit chord marker properties is just like the section markers' dialog except the Text property is replaced with options that are used to name a chord. As shown below, there are four columns that represent the parts of a chord's name. You need to select one item in each column.
Tidying up marker start and end times
You can have Song Master tidy up the start/end times of all or just a selection of chord markers. In the demo below, we first change the snap to setting to beat so the start times will be moved to the closest beat. We then click the Fmaj7 marker and then shift-click Dm to select all markers between them. The context menu allows us to just tidy up the selected chords while the track header's menu gives us an option to tidy up all markers: