Click http://www.mikesmusicroom.co.uk/chordbook.html to learn how to play 7th chords and download the complete keyboard chord book which includes 12 major chords, 12 minor chords, 12 seventh chords and 12 minor seventh chords.
The three 7th chords in this video are:
C7 Major Chord
G7 Major Chord
D7 Major Chord
Used Electronic Keyboards For Beginners - Auction Page:
http://musical-instruments-uk.mikesmusicroom.co.uk/Keyboard-Piano/Electronic-Keyboards