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At the prompts "Name:" and "Description:" provide text that relates to the customisation you are about to perform, then at the prompt "Customisation Type:" select which portal is to be customised, then at the prompts "Agents:" and "Applications" click on the search icons (see arrow in the picture above), then select the agent and application that matches your selected customisation type;
You can now prepare the customisations using the section headed "Manage Content";
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