There are 2 ways to remove the contacts from the Automation.
1. You can remove them from the bulk action. To do that, please select the contact, click on bulk action and select Remove from Automation.
Please check the video:
2. You can create a workflow and add a node "Remove from Automation" and select the automation. Save the workflow.
Once the workflow is ready, please add the contact to the workflow and it will be removed from the automation.
Please check the screenshot of the Workflow:
Please check the video: