iMovie 10.4.1 Cannot find the Audio Rubber Band tool

I am editing a documentary film with background music. I wish to drop the volume of the background sound during a narration to enable the narration to be heard clearly without interrupting the music. In previous releases of iMovie I was able to fade the sound by clicking the Audio Waveform and inserting handles in the shape of a lozenges to mark four points, start of fade down, end of fade down, start of resume of normal volume and end of resume volume. these handles could be positioned within the waveform to synchronise with the pre narration and post narration period. This was called the Audio Rubber band tool in various publications. I cannot find this facility in iMovie 10.4.1 with current Operating System Sonoma 14.6.1.

Is there another way of performing this function?