1- On the guide's step, click the reselect icon.
2- To reselect an element you have 2 options, as displayed below:
Option 1: Re-select on screen
Modify an element by selecting a new one directly on the webpage. When you click on the step number it will turn blue and then you can select directly the new element.
Option 2: Re-select manually
It is possible to HTML selector to select specific elements on your web pages on which you want to add a guide step. This option allows more precision when selecting your own website's elements. You can use the web inspector of your browser to take a look at the corresponding HTML selector.