Getting a Ugandan document legalised - apostille?

My son has a Ugandan birth certificate and lives in Europe. He needs to present his birth certificate legalised with an apostille. Can anyone offer advice on how he gets that done, please?

You will need to contact the Ugandan Government department responsible for registering births and request; they are the only people who can "Apostille" his birth certificate.

Thank you. That dept appears to be NIRA so I have emailed them for information. There is nothing I can see on their website concerning it.