Hi @venepress-web,
Go to ‘Appearance > Customize > Widgets’. There the list of widgets area are shown as related with the Customizer Preview on right. (The Right Siderbar or Left Sidebar widget area will not be shown if the customizer preview is showing ‘Front page template’). So from the customizer preview click and go to the post or page single then after that ‘Right Sidebar’ or ‘Left Sidebar’ widget area will be listed on widgets of customizer option on left (if only the layout is not set to ‘No Sidebar’ or ‘Full width’). Then you can edit the widgets on the respective widget area as usual.
Thanks
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