If the metadata extension you want to edit is reusable and editable, you can change the value of the metadata extension, but not any of its properties. However, if the vendor or user who created the metadata extension did not make it editable, you cannot edit the metadata extension or its value.
To edit the value of a reusable metadata extension, click the Metadata Extensions tab and modify the Value field. To restore the default value for a metadata extension, click Revert in the UnOverride column.