This can be done in multiple modes.
You can unlock this in Driver Mode, Team Mode, or doing Solo Grand Prix or Championship, driving as your favorite driver, in Practice, Qualifying or Race.
Difficulty and Assists do not hinder at all, as you can obtain this while the DRS Mode is AUTO (as i did, as i forgot my 6 year old Nephew wanted to have a shot xD). You can adjust that in your Assists Settings.
You will see while you are driving, on the bottom right-hand side of the screen, a DRS countdown, then it will glow yellow. Hit
and DRS is activated.
Do this at all the zones (basically everytime DRS is shown on your screen) at the first moment you can, and the achievement is yours. You will notice, while racing, a white DRS sign on the side of the track.
There is a programme during practice that focuses on this if you can't do it during a race.
It may take some time to get used to, and may not unlock at your first try, but you will get there :)