You could use a passive resistor divider such that the voltage is divided down to about 4V (full-scale range of the Bela ADC is 0V : 4.096V, absolute minimum and maximum range is 0V to 5V).
+---- Va (Bela analog in)
Va = R2/(R1 + R2). You will want R2 to be at least 1k. Using common resistor values, you could have R2 = 4.7k and R2 = 2.2k, so that
Va = 2.2/(4.7+2.2) = 0.319.
If you are doing this for Eurorack purposes and you need variable attenuation on your input, you could have a look at our Pepper module, either to use the full module or just to have a look at the schematics. There we have a 100k resistor followed by a 50k potentiometer:
C4 is an optional 150pF capacitor which acts as a low-pass filter on the input.