To be able to use your Evvnt assets as a child assets in BLOX, you will need to set up an importer to bring them in.
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Content Importers automatically syndicate content into BLOX. Once a Channel has been established, the Search terms panel can be used to query content with specifics, such as asset type, category and date. That criteria can then be used as the basis of a Content Importer for automatically pulling in content on an ongoing basis.
This article describes working with the BLOX Digital Content Exchange Syndication Channel.