Transform one voltage range to another
You need another resistor (from the non-inverting input to ground)  if attenuation is required. Call that Rs.
Let's pick R1||R2||Rs = 10K
Then we can immediately write:
(12V/R1)*10K = 0.8V so R1 = 150K
The output will be zero when the input is -(1/8)*12V or -1.5V.
So Vref/R2 = 1.5/150K by KCL. Say Vref is 5V then R2 = 500K (499K is closest E96 value)
And finally Rs is 1/(1/10K - 1/150K - 1/500K) = 10.95K.
(and Rf = 10K, Rg = open)  -- Rf = 10K cancels out offset component from input bias currents if they are equal.



simulate this circuit &ndash; Schematic created using CircuitLab