From Contacts SmartList (Bulk or Individual)
Go to Contacts → SmartLists.
Check the tick box next to the contact(s) you want to add.
Click the "Add to Automation" icon (looks like a robot) in the top menu.
Select the workflow from the dropdown menu.
Choose to add immediately, schedule, or use drip mode.
From Inside the Contact Profile
Open the specific contact record.
Scroll to the "Campaigns and Workflows" section.
Click "Add" under active workflows and select the workflow.
Within the Workflow Builder (Testing)
Go to Automation and select your workflow.
Click "Test Workflow".
Select the contact to run through the workflow.
Key Tips
Ensure Published: The workflow must be in "Published" mode to add contacts manually.
Remove Contacts: To remove someone, go to the contact record and click the remove option under "Campaigns and Workflows" or use the enrollment history inside the workflow.
Action Name: You can name the action to track it later in the Bulk Actions log.