To silence the bass for half a bar, add a dot (which causes a rest) after the chord, then the initial of any parts that you do want: p (piano) g (guitar) d (drums) etc.

For example, if you want piano, drums and bass for the first half of the bar, and only piano for the second half, and the chords are G major seventh and F9, you'd enter GJ (J is the shortcut for major &th) then F9.p

Hope this solves your problem.

Mike Laatz
Cape Town