To add metadata that has an already-existing value, first select the file and then select the required value from the value tree, expanding subject folders as necessary. The value of any selected entry in the tree automatically appears in the Value text field. Alternatively, you can use the auto-select and auto-complete features of the value tree. Click [A]dd to add the metadata to the selected file.

The process of adding metadata with already-existing values to directories or multiple files is just the same.