If you access your email via your web browser, go into its setting and delete the stored password. (If you've not stored the password, you won't have a problem anyway). If you need instructions, please tell us which browser you're using.
If you access your email through a dedicated app though, such as the Windows 10 Mail app or Thunderbird, things could be a little trickier.
One technique that would work for both webmail or app access though is to create a separate Windows account on your laptop. Then password protect your original account, so that the technician can only access your laptop through the new account.