Hey, welcome to the forum
Even as a bassist, I’m sure you’ll have your new toy reaching the octave you’re aiming at. Pardon me if what follows is obvious to you.
For one, the transpose buttons are on the left, bottom part of the panel.
For two, each one of the two oscillators can be set on four octave (I’m not talking about the pitch range of the instrument that is 10 octave wide or so).
Here is a way to get low.
With the transposition buttons, start by setting the keyboard on the center octave.
Now, synthesis-wise:
In the mixer section, set all levels to zero except the oscillator 1 one; leave it half way.
In the oscillator 1 section, set the octave switch to the lowest pitch setting.
At this point, have a listen and use the transposition setting to have the keyboard playing in the pitch range you like.
If -despite the lowest of lowest settings- it’s not low enough, ask yourself if you’re expecting lower pitch or darker tone.
For lower pitch, try to add a bit of Sub oscillator in the mixer section.
For darker tones, check the MultiDrive is set to zero or low, play with the filter cut off setting and take care not to mix your sources (oscillators…) beyond half way or so as the mixer is designed to saturate a bit when overloaded.
Hope this helps!