Hi iniwoni,
First of all, as to your term "label" for color scale bar, I suppose you mean "title" in fact? see screenshot below.

On the Color Scale Control dialog, the "Labels" is used for the tick labels.
If yes, you may try py script below.
import originpro as op
gp = op.find_graph()
gl = gp[0]
sp = gl.label('SPECTRUM1') #name of the color scale bar
sp.set_str('title', 'testA/testB')
If you do mean tick labels, it is not supported yet and we will take a look. (internal record ID: ORG-31409)