There's no way to isolate the words automatically, but you can split-out the "umms" and then apply the AMPLIFY effect at zero gain to all at once.
Play the timeline and press the L key at the start and end of each word to be deleted. If you make a mistake, press <ctrl-Z> to backtrack step-by-step.
When all have been isolated, expand the timeline with the slider at the bottom-right to better see the individual clips.
Select all the "umms" that you isolated by holding down the <ctrl> key while clicking each.
Right-click the FX icon in any one of those selected audio track clips, choose the AMPLIFY effect. Set the slider at zero, then click the "replace chain' button.
All selected clips will be muted. Video will be unchanged.