Hi @jascanio
To assign DOI, even existing ones, you should follow instructions as follow from this thread:
Configuration of the DOI plug-in is done though this path:
→ System Plugins → Public Identifier Plugins → DOI plug-in → Settings.
Wil be necessary paying attention to your DOI pattern or your “mask” DOI. You will need/have to copy such pattern to be applied in those articles metadata.
More info here:
https://pkp.sfu.ca/wiki/index.php/DOIPluginsDocumentation#Configuration_of_the_DOI_plug-in
Regards,
Israel Cefrin
Public Knowledge Project Team