The IIIF Server module for Omeka S allows you to configure various settings. One of these is the attribution setting.
As shown below, the value entered in Default attribution will be displayed in the attribution field of IIIF manifest files and similar resources. I recommend changing it to an appropriate value such as your organization’s name.

Alternatively, as shown just above the field mentioned above, you can specify a property for entering attribution values, which allows you to change the attribution value for each item individually.
I hope this serves as a useful reference when using the IIIF Server module.