Press
and go to Customise. Changing anything and saving is meant to unlock this.
I customised my character multiple times and this wouldn't unlock. In the end, I created a new character using a preset character and changed nothing. I switch to that character and then changed their Gender and an item of clothing. On saving, the trophy unlocked.
I then switched back to my original character and continued playing. This doesn't lose you any progress, so there is no worry there.