NOTE: This refers to the "Credits (Attribution)" field for items, regarding users who have contributed to content, not Credits, the currency in ArcGIS online.
The following is a workflow that requires the Pro Version of Admin Tools:
In Admin Tools, in the Items category, under Export, select the tool called Export Items to CSV:
Here, you can export various fields. In this case, we'll be using "Access Information," which should be checked by default.
From there, open the CSV file in excel, adding the names of the people you'd like.
Save the file using the CSV format (keeping the commas).
Next, in Admin Tools, in the Items category, under Import, select the Import Items from CSV tool (in our Pro version) and import the updated CSV file.
Now, all your Credit (attribution) should be updated for your items!
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