If you are on PC, then go into your controller options where you can re-map keys if you wish.
The default for the PC keyboard is this :-
Click any of those 1.2.3.4 keys to bring up the menu when you are driving. Then make your selections from there.
I can't remember the menu from memory, but it might be like like.
You want Fuel Rich?
Menu - Press 1 (up) {or any of those 4 keys}
Fuel - Press 1 (up)
Rich - Press 1 (up)
= 1,1,1
Fuel to Standard?
Menu - Press 1 (up) {or any of those 4 keys}
Fuel - Press 1 (up)
Standard - Press 2 (right)
= 1,1,2
Some have a DPAD on their wheel that does the same thing e.g Logitech Driving Force GT. So for that 1st example above for rich fuel would be
DPAD Up, DPAD Up, DPAD Up - Consoles are probably like this too.
You can remap those keys if you want. Typically you might remap the 1,2,3,4 keys to the 4 arrow keys on the keyboard insteaad, because they are more natural to use. i.e up arrow, up arrow, right arrow
I hope that's clear enough for you