There is a drop down menu for making chords; click on the arrow at the chord window for the letter of the chord, once it appears, click on the arrow again for the qualities to list.
However you might find it easier using the Mac keyboard for at least some of the input, especially for some of the more common chords. For example C7 I find it easier to just type in a letter 'c' then '7' than clicking the menu, or c 6 9 for C6/9 etc.

You can use the Return key on the Mac keyboard to move along. Using the other key commands as outlined in Bob's link in the previous post, you can get quite fast for editing or input.

Tip: if you are editing an existing chord, you do not have to delete it, just use the Mac keyboard to enter the chord's letter then add the quality.