Click on the desired hub group in the table. On the hub group’s page, click on the Bulk Add button and paste/type in the desired hub ids. Make sure you type at least 10 characters:

<aside> 💡 This feature is meant to make it easy when copying a column of hub ids from a CSV/Excel file into the text area, since the hub ids can be separated by commas, whitespace, or newlines.

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Clicking Add will move all the desired hubs into the current hub group.