1)

Add proper URL rules and select "Digital Duct Tape"

2)

Select the area which you want to hide and apply duct tape to

Click the color palette to change the default color and choose a color to cover the area

3)

Select this checkbox to enable the alert for duct tape

As soon as you select the checkbox, editor will be enabled where you can provide a message

4)

Click on "Save"

5)

Publish the tooltip!

6)

Here is the duct tape in action. 
Click on it to view the alert message

7)

This is how the message appears, click "Ok" and note that after the popup disappears the area hidden under the duct tape will start showing

8)

Similarly, you can also hide the area by making it transparent. For that, you need to select the radio button for "Make element invisible"

Also, for this option we don't get the alert checkbox

9)

Click on "Save"

10)

Publish the tooltip!

11)

Notice that the area you've selected, is invisible