can i add a new baby onto an existing ancestry visa

Hi there

Have had a uk ancestry visa for almost 3 years been back in canada with my husband and 2 daughters and due to my husbands new job we are heading back to the U.K we all have the Ancestry visa in our passports BUT since back in canada I have had a new baby.

How do I add my newborn onto my existing ancestry visa? I am puzzled as it all seems to point to a new application. Surely we dont need to reapply as our ancestry visa is still valid

Any help please?