Metadata default values - Content tool
Document metadata defaults can be set using either the content tool or the portal.
Metadata defaults can be inherited from the document category or metafield group defaults. In these cases, the metadata field value is disabled but can be overridden by clicking the link button to the right of the field.
How to set default value
Using the content tool, the default values for document metadata can be changed by opening the desired content and clicking the Information button in the toolbar. Then select Default values tab.

When a metadata field is enabled, its value can be set. If a metadata field is disabled, its value is inherited from the document category or metafield group. To enable / disable field click the link button on the right side.
Once the default value is unlinked, changes made to the document class or metafield group are no longer inherited. You can restore the default value by clicking the link button again.

After changes click Save button. If you only want to change the default values, you don't need to use Update file from the toolbar.