Hi Earl,
I guess, your keyboard is still the PSR-3000.
If you don't need an automatic accompaniment (the Style parts Bass, Chord1/2, Pad, Phrase1/2), you can simply switch OFF the ACMP button. Then you will have only the Drums (Rhythm1/2 parts of the Style) and can play the BASS with your left hand (Left voice) and the melody or "fill" with the right hand.
You could also try to set the fingering to "Full Keyboard". Maybe you can play the Bass with your left hand then and also switch ON the ACMP button to use the complete Style accompaniment. The PSR-3000 manual says:
Detects chords in the entire key range. Chords are detected in a way
similar to Fingered, even if you split the notes between your left and
right hands—for example, playing a bass note with your left hand and a
chord with your right, or by playing a chord with your left hand and a
melody note with your right.
In newer models (like Tyros5, Genos, PSR-SX) you can set the Chord Detection Area to "Upper". But the PSR-3000 doesn't have this feature.
Best regards,
Chris