The G flat altered chord is a 4-note chord consisting of the notes Gb, Bb, Fb and Abb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gbalt7.
Chords that are a superset of Gbalt7. The chords include more notes but always Gb, Bb, Fb and Abb.
In case you prefer a non-interactive variant of the chord chart, we've embedded a PNG image below that shows the notes for the the Gbalt7 chord. Feel free to save or share the image as needed.