Then you need to edit the template that actually displays your calendar and change the link to the event’s detail page to your custom field’s one as described above. Only I don’t know if the plugin is actually working with editable templates or not. Usually there are template files included with the plugin or you can create a new one, but that depends on the plugin you use.
Do you have a basic notion of how to actually use the custom fields you create with ACF?
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