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With the new data source added, right-click on a data source in the pane, or open the Data menu, and then select Replace Data Source… from the menu that pops up (you will need to do this from a sheet rather than a dashboard):
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After selecting this value, a new window should pop-up that lets you select which Data Source to replace. Make sure the “old” data source is listed first (as “Current”), and the “new” data source is listed in the “Replacement” drop-down, and click OK.
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