Triggering an automation for existing contacts
If you've set up an automation with the Contact added trigger, you might notice it didn't trigger for contacts who were already on your list before the automation was activated. That's expected – Contact added trigger only works for contacts joining your list after the automation is active. It won't pick up existing contacts, even if you tick the option to include imported contacts.
If you'd like the automation to include the subscribers already on your list, use the Contact tag added trigger, then add that tag to your existing contacts so they enter the automation.
If you already have an automation and you're on a paid Pro plan, you can add an additional Contact tag added trigger to replicate the scenario described in this guide. Learn how to do that here.
To do this, you need to create an automation with the correct trigger. From your dashboard, go to Automations and click Create.

Next, choose the Start from scratch option.

Set up your automation's name. Choose the settings you want to use for this automation and click Next.

On the trigger screen, select the Contact tag added as your trigger.

Choose the tag you want to use, or create a new one (in our example, it's "Send welcome series") and click Finish setup.

Add your automation steps (automated emails, waits, conditions, and actions) as usual, then click Start to activate your automation.

Contacts will only trigger the automation while the automation is active, so make sure you activate the automation before moving to the next step. Contacts tagged before the automation is activated won't trigger the automation.
Now, add the trigger tag to the contacts you want to enter the automation. This can be done in the dashboard, using list Actions, or via import. You will find instructions on how to do both here. As soon as the tag is applied, each contact will enter your automation.