This isn't as hard as i originally thought it could be
From the Home menu, toggle
to "Solo" and select "Time Trial".
Choose whichever series you like, F1 2020 obviously being the current(ish) drivers.
Select your team/car and driver (in F1 and F2 series), or an older car in the Classic series.
You can then select your favorite track, along with your assists. I personally chose Britain Short, as it's a cool little quick circuit :)
Default Ghost for me was over a minute and pretty easy to beat (that might be reflective of yout AI levels, i'm not sure). Don't push it the first lap (to set a lower time), but then go for it on the second, being able to easily beat your PB.
The Rival Ghost shows up after your first time, which as i didn't go all out, that was pretty easy to beat as well.
Achievement unlocks after you beat the Rival Ghost (and while i was still out on track)