Tags in automation

Hello,
I created an Automation, and I used tags to filter the contacts that I need/trigger the automation… although, the contacts only enter the automation if the tag is entered after the Automation is active. The contacts that already have the tag before the Automation was active, don’t go in the automation automatically… Do you know any magical trick to make the contacts that already have the tag, get in the new automation other than retagging them all?
Thank you