If you click Change tool bank, you can select the Draw note tool. Try drawing in the two notes, that the arrows are pointing to, directly above the original C note (the new notes are E and G) to make the last chord.
Now do the same thing for the middle chord: use Suggest a chord to point to the notes of 'G maj' (G major) and then use Draw note to draw in the two notes above the middle note -- G. The new notes are B and D.
