Open your Slack workspace in any web browser. If you use the Slack app on your laptop, clicking on your workspace name with the dropdown arrow at the very top left of Slack should show you the URL to type into your browser.
The browser will redirect you to a different URL and open your workspace.
You can now find your Team ID in the URL. It will begin with the letter T and be 11 characters long, e.g. https://app.slack.com/client/T04FTGB9SD3/C03K3382.
That's everything! If we've asked you for your Slack Team ID, here's how you find it! If you have any questions, please do get in touch!